# CO2 In the planted Aquarium



## aaronnorth (13 Jul 2008)

Carbon Dioxide (CO2)
Plants are made up of 50% carbon (dry weight). Submerged aquarium plants absorb carbon through carbon dioxide (CO2) dissolved in the water. All aquarium plants will benefit greatly from adding CO2 to the water. For those wanting to keep a heavily planted tank, full of lush growth with little or no algae then I consider CO2 addition to be almost essential. 

WHY HAVE CO2

Under low light conditions (generally less than 2 Watts per Gallon) there is normally enough CO2 for the plant to grow successfully without CO2 addition. If the light levels are increased to over 2 WPG then the plants will grow well for a period until they consume the little CO2 (normal levels are around 6ppm) that is available in the tank. The plants growth is then limited by a lack of CO2. The plants will stop growing, resulting in an algae bloom because of the light and suspended nutrients. Algaeâ€™s biggest friend is a tank where there is lots of light and little plant growth. It therefore becomes necessary to increase CO2 levels within the aquarium. CO2 addition (injection) is therefore recommended with light levels of 2 WPG or over. The high lighting â€˜drivesâ€™ the plants to uptake more CO2 and nutrients (see Lighting article).

METHODS OF INJECTION
Yeast-Based
The cheapest and a popular way is to DIY. DIY generally uses an old plastic fizzy drinks bottle with tubing. The bottle is filled with a mixture of sugar, yeast, water and bi-carbonate of soda. The fermentation of the yeast produces CO2. The CO2 goes through the tubing that is normally attached to a diffuser or under the filter inlet within the tank. The CO2 must be diffused effectively in the water, it cannot just be allowed to escape from the tube directly into the water otherwise the CO2 bubble will just rise to the surface out of the water. Here is a guide on how to build a DIY CO2 system:

http://www.fishforever.co.uk/carbondioxide.html

http://www.aquatic-eden.com/2006/10/bui ... rator.html

There are manufactured CO2 systems that work using the same fermentation process. These are slightly more expensive but have the advantage of being easier to set up and come complete with an effective diffuser. The Nutrafin Natural Plant System is a good example. The manufacturerâ€™s supplied sachets are simply yeast and bi-carbonate of soda. It is worth noting that bi-carb is unnecessary with water that has a GH of 6 or above and KH 4 or above. 

I would recommend to use more than one unit (DIY or manufacturer system) to achieve a more stable CO2. This is achieved simply by swapping the mixtures alternately, one at the weekend and one midweek. Also I would chuck the mixture supplied with the Nutrafin system as the yeast is produced to last longer than normal unlike bakerâ€™s yeast. Another option is to use brewerâ€™s yeast which can support a higher alcohol content so therefore lasting even longer.


Pressurized Cylinder
Another more expensive method is the pressurized cylinder. A CO2 filled metal refillable or plastic disposable cylinder is connected to a pressure regulator. This brings down the pressure to usable levels and can be adjusted to achieve the desired flow rate using a needle valve. The CO2 hose is can be connected to a solenoid which can be timed to turn off at night to save CO2 as plants donâ€™t use CO2 at night. It also stops the ph dropping to low which could be fatal to your fish (more on this later). Then to a bubble counter (BC). The BC counts the bubbles produced per second (BPS) or per minute (BPM).A safety check valve is fitted to ensure no backflow of the aquarium water goes into the solenoid or Gas canister. Finally the CO2 flows to a diffuser or reactor. Initially these are expensive, these will provide a constant CO2 flow for many months (depending on tank size, planting density etc). A pH controller can be fitted, this will continue to inject CO2 until the pH drops to a preset level. A solenoid will then shut-off the CO2 supply until the pH has risen to the preset level. This provides a very stable pH. However, the downsides to pH controllers far outweigh the advantages of a stable pH (which isnt actually necassary in itself!). CO2 injection will drop the pH by approximatley 1 unit - fish experience pH swings much larger than this in the wild, one example is acid rain. Also, the CO2 being switched on and off constantly causes instability which may lead to algae problems. Finally, a pH controller may actually limit carbon to the plants. For example, you decide you dont want the pH to drop below pH6.5, and your tap water is pH7. Before you can inject 30ppm of CO2, the pH controller will cut it off due to the pH being to low!! you may only be able to inject 20ppm in that time period.

Liquid Carbon
Becoming increasingly popular is liquid carbon. It isnt actually carbon, but a complex carbon compund made up of glutaraldehyde (C5H8O2) as a base foundation, this goes though various chemical proccesses and it is fixed into carbon using the calvin cylce. Liveworts, Bladderworts & algae do not have this function, so instead it becomes toxic to them. most plants are fine with the reccomended dose, but then they rot if they are raised. Particular species include:
vallisneria
riccia fluitans
utricularia graminifolia
egeri densa

Liquid carbon is an excellent alternative to other CO2 methods, but it is worth mentioning it isnt as effective as CO2 gas alone. It can be dosed alongside other types of CO2 injection methods. It is very cost effective on small tanks.

Yeast is Cheap to set up, but may cost as much or more in the long run, it is ideal for smaller tanks and easy to set up. There is also little chance of overdosing CO2. Some disadvantages of yeast based system is that there is unstable CO2 levels compared with pressurized which could cause algae, there is high maintenance (changing mixtures, cleaning etc.) and little control over CO2 output, not ideal for larger tanks as lots of bottles are needed.

With pressurized, you get very stable CO2 (especially with a solenoid), it is easily controllable, it is low maintenance (once set-up it will last months depending on size of tank and plant mass), it is ideal for all sizes of aquarium, no matter what size, whether it be 1 or 1000gallons.

It is expensive initially but cheaper over the long run and there is a possibility of overdosing CO2 but it is easily adjusted to bring it under control. Once the pressurized system is set up, the pressure may drop so it may need tweaking a little but it should be rectified within 48 hours.

You can also do a DIY pressurized system, as long as you leave the safety pin in, dont press the handle, and don't knock it over then everything is ok.

Fire Extinghuisher CO2

Courtesy of Sam (themuleous) for writing this excellent Guide.

LEVELS OF CO2 IN THE AQUARIUM
Recommended levels of CO2 are 25 to 35ppm. It is important that these levels remain fairly constant, as fluctuating levels are known to cause algae. Higher levels are sometimes used to fight off algae; it is known that levels higher than 40ppm can block the enzyme production in the algae cells. However you must watch the behaviour of your fish high levels can cause problems.

One of the consequences of injecting CO2 into water is that it produces carbonic acid. This acid will reduce pH (generally by 1 on the pH scale) so it is important that the water has sufficient buffering capacity (Carbonate Hardness or KH). Ideally the water should have a KH of at least 2 degrees or 40ppm. 
However, people have reported no problems even when using 0dKh water!!

using pH/ KH relationship charts is a very innacurate way of measuring CO2 levels. Tank water contains other acidic substances, which can affect the reading. Even Nitrate and Phosphate can!
As the CO2 gasses off from the aquarium into the drop checker, the ph lowers due to the carbonic acids formed by CO2 when it dissolves in water. When the drop checker turns from blue, to green, this indicates a pH of 6.6, and because we know the solution is 4dkh, this tells us we have approximately 30ppm of CO2 in our tank water.
If you are using a 5dkh reference solution, then a pH 6.6 (green drop checker) will indicate 38ppm.

Another way of measuring CO2 is to use a drop checker (DC), You fill the ball with 4DKH solution (make it yourself or get it from Aqua Essentials ) You then add a couple of drops of bromothymol blue or low range pH test to the 4DKH solution. This should then turn blue. Turn it the correct way up and place in the aquarium, the air bubble (forms automatically) will stop the solution mixing with the tank water.
CO2 measurment usng a Drop Checker
A benefit of CO2 is that the reduced pH levels can often be beneficial to a lot of tropical fish. The majority of freshwater tropical fish originate from water with soft and acidic water, examples include Tetras, Rasboras, Angelfish, Discus, Barbs, Corydorus, Loaches, Killifish, Gouramis, Bettas and most species of Catfish i.e. Plecs.

Blue - low CO2 (less then 20ppm)
Green - Ok (between 20ppm & 35ppm)
yellow - too much (over 35ppm)

PH SWINGS
During the day (when the tank is lit) the continuous injection of CO2 causes the pH to drop as carbonic acid is produced. we usually use a solenoid to cut the CO2 off at night, which means the pH would then rise as the CO2 gasses off, but if you dont, then the pH will remain fairly constant.
Injecting CO2 usually causes a drop in pH by 1 unit.


DIFFUSING CO2 INTO THE WATER

CO2 is quite unstable in water and it must remain in contact with the water for it to fully dissolve. There are devices that help with this and these are called diffusers or reactors. There are many types of diffusers available ranging from a simple bell-jar, where the CO2 bubbles simply collect and dissolve over time. A more popular method is a ladder-type device where each bubble travels up through a series of rungs, the bubble remains in contact with the water for longer and  the water absorbs the CO2. This process is visible as the bubbles get smaller as the diffuse into the water. The Nutrafin kit comes with a ladder diffuser. 

In larger aquariums the common diffusers are not really efficient and another method is the reactor. They are not self-driven and rely on a source of flow for the CO2 to dissolve effectively. Reactors are normally associated with pressurized CO2.

Common types of reactors are fitted in-line with the external filter output. The CO2 is produced by the pressurized cylinder and flows into the reactor. The reactor is filled with some form of media that allows the CO2 bubbles to dissolve fully where the CO2 enriched water is then pumped into the aquarium.

A really simple method of CO2 reaction is to use the external filter; you can run the CO2 output directly into your external filter inlet. The bubble diffuses through the filter media and the CO2 enriched water flows out into the aquarium. The only disadvantage is that it can make a slight noise when inside the filter. It is still quiet though.

CO2 AND OTHER NUTRIENT FERTILISATION

If you have over 2 WPG of lighting with a stable CO2 level of 20-35ppm then plant growth will be fairly rapid. Especially if the plants are a fast growing species (particularly stem plants). The rapid growth results in the plants using up various and more nutrients. These nutrients need to be replenished by a fertiliser; otherwise the plants stop growing leading to algae. Therefore fertilisers need to be added regularly. 
EI using dry salts

Injecting CO2 in an aquarium no matter how much light you have will help, even low CO2 is better than no CO2. Please ask for specifc information on your tank in the planted section.


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## beeky (1 Aug 2008)

Nice work, cheers for that.

I'll mention here that the disadvantage of pH/KH/CO2 tables are that other acids caused by bogwood and decomposition can effect the results. The tables referred to assume carbonic acid is the only acid present. That's why drop checkers are increasing popular as the use of 4dKH water is more accurate. They can also be mis-interpreted by people summising that if they change their pH or KH it can effect how much CO2 is in the water.


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## Themuleous (1 Aug 2008)

Nice one Aaron


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## LondonDragon (4 Aug 2008)

Nice write up Aaron


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## Wolfenrook (9 Aug 2008)

Not bad, but you have a pretty hefty bit of falsehood right at the start:-



> Almost half of the plant is made up of carbon,



Seeing as how plants are about at least 80% water, it would be a bit difficult to have 50% carbon in there as well.   

Ade


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## aaronnorth (10 Aug 2008)

Wolfenrook said:
			
		

> Not bad, but you have a pretty hefty bit of falsehood right at the start:-
> 
> 
> 
> ...



i'm sure it could squeeze in   

I'll change it


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## Brenmuk (10 Aug 2008)

In the Ecology of the Planted Aquarium it states that aquatic plants are about 40% carbon, that is 400, 000 mg C/kg plant dry weight. When looking at feeding plants it is helpful to consider their composition in terms of dry weight so that we can get a better idea of the nutrients they need. 
 You might want to change it back to your original statement but qualify it as dry weight  

Brendan


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## aaronnorth (10 Aug 2008)

Brenmuk said:
			
		

> In the Ecology of the Planted Aquarium it states that aquatic plants are about 40% carbon, that is 400, 000 mg C/kg plant dry weight. When looking at feeding plants it is helpful to consider their composition in terms of dry weight so that we can get a better idea of the nutrients they need.
> You might want to change it back to your original statement but qualify it as dry weight
> 
> Brendan



ok, i can feel a big dispute coming on


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## Wolfenrook (10 Aug 2008)

Not so much a dispute, but dry weight is misleading as to most this just means not wet.  More accurate would be to say 405 carbon when dehydrated, as even when 'dry' the cells of plants still include about 80% minimum (most plants it's closer to 90%, it's actually animals that are about 80% water) water in the construction of their cells.  I really couldn't care less if a book choses to make scientifically inaccurate statements, this still doesn't make them true, maybe the author needs to go back to school and do his basic biology again? 

Ade


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## Egmel (14 Aug 2008)

Wolfenrook said:
			
		

> dry weight is misleading as to most this just means not wet.


I disagree, usually when you buy something 'dry weight' means the weight without fluids, be that water or otherwise.  I'd be quite happy with that term and if you want to be totally sure just link it to the wiki page as I've done.  There's no point not using the correct term because it might be misunderstood, better to use the correct term and educate the reader, or is that just a perpetual student's view


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## vauxhallmark (14 Aug 2008)

Egmel said:
			
		

> Wolfenrook said:
> 
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Wolfenrook, I agree with your argument completely, _except_ for the words "fluids, be that", and "or otherwise". Dry weight (in this context) does mean without water, not without any other fluids. Mercury at room temperature is a fluid, but completely dry. The same goes for dry cleaning fluids (!), petrol or the liquid CO2 in your cylinder (and if you froze that, it would be dry ice).

You're right, though, that the term dry weight is the correct one, and, as you say, I think most people would understand it in the article above to mean "with all the water removed", and not "after wiping water off the leaves"

Go perpetual students!

Best,

Mark


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## Egmel (14 Aug 2008)

vauxhallmark said:
			
		

> Wolfenrook, I agree with your argument completely, _except_ for the words "fluids, be that", and "or otherwise". Dry weight (in this context) does mean without water, not without any other fluids. Mercury at room temperature is a fluid, but completely dry. The same goes for dry cleaning fluids (!), petrol or the liquid CO2 in your cylinder (and if you froze that, it would be dry ice).


Difficult one, it depends on what you're buying, cars and bikes are quoted a dry weight so that the fuel and oil's don't count.  In the context of almost anything else though you're absolutely correct, it's without water.


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## vauxhallmark (14 Aug 2008)

Egmel said:
			
		

> vauxhallmark said:
> 
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Mmm, yes ... that definition (vehicles) is already listed on the Wikipedia page quoted by Wolfenrook two posts back. I specifically said "in this context" the first time I referred to the term, and "in the article above" the second time.  Nobody could think that "dry weight" in the original post could refer to plants with an empty petrol tank, and unlubricated by moter oil ... or could they?


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## Ed Seeley (14 Aug 2008)

Dry weight in a scientific context such as this article refers to is generally the dessicated weight of a sample.  To obtain such a weight the sample is dried at a low heat until it's weight ceases to drop.  This is then a sign that all the liquid water has been removed from the sample.  It can then be sampled and tested to determine the other constituents of the matter such as protein, fat, and other materials.


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## aaronnorth (15 Aug 2008)

do you think i should put the amount of carbon a plant is made up of in dry weight o just leave it?


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## plantbrain (15 Aug 2008)

Wolfenrook said:
			
		

> Not bad, but you have a pretty hefty bit of falsehood right at the start:-
> 
> 
> 
> ...



In standard analysis of nutrients/atoms, all percentages are as dry weights, otherwise, how could anyone compare due to variation in water status? If you have an answer that's easy to do, I'm all ears, you can make a wet to dry weight correlation, but it depends on th methods and the plant and specific for that study and hopefully no psuedoreplication occurs.

Most dry weights from macrophtyes fall into 40-50% ranges.
Next largest is N at perhaps 1-2%.
See http://www.bestwebbuys.com/Mineral_Nutr ... c=b-search
Arnold Bloom is a past professor of mine here at UC Davis and the co author above.

Having done and am doing dry weights several times a year for various projects, you can also make a dry to wet weight correlation factor as well. We typically dry most at 70C for 48 hours for most aquatic plants unless there's a really large thick tuber or something. Then you weigh it, grind it and send it to the nutrient analysis phase for % N, P, Fe or Carbon etc.

For non destructive sampling, you take O2 readings and use that to relate to rates of growth.
Or CO2 uptake relative to the location of CO2 meter.

and so forth............
So if you use your own over and can set it to 70 C fairly well and keep it there for 48 hours etc, you can do this, or if you have access or can bribe someone at a plant science lab to dry it for you, have access to an accurate scale, any hobbyists can do the weights.

You sample, you dry and a you weigh.
Not high tech or anything.

But you need to have a standardized starting weight, so the correlation between wet weight starting values and dry weight is important, but again, this is not hard to do. You take 20 sub samples(or 5, 10, 100 etc however good you want your stat's to be that is practical), and weight the before and after dry weights, then use that ratio to gauge the differences in the starting weights of the live plants.

So say you want to measure 100 plants' response to CO2 enrichment for 8 weeks. You need 120 plants/stems all about the same relatively. You can weight and measure their length(you can make a dry weight to length ratio as well), and take that 20 subsmaple and dry them BEFORE you treat and grow them out. This gives you the starting reference point.
So this way you can make a relative rate of growth, often called RGR to compare across treatments without having to kill and dry your plants along the way.

Plants get much larger as they grow and often in exponential fashion, so adding 20ppm when the tank is first planted might be fine, however, 2 months later, when the biomass is now 800% more and the tank is fairly full, you might need to add 7 X the same amount of CO2.

If you trim and garden routinely, then this is not an issue, it's when folks neglect CO2 and the tank in general, let things go too long, that we see issues.

This is especially true for higher light systems and where we use CO2 gas as well.
increases the rates of growth and speeds everything up, which might not be your goal in aquatic horticulture(or might be).

Regards, 
Tom Barr


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## brian68 (16 Sep 2008)

I have a 200L tank and am injecting pressurised CO2.  One thing I'm not clear on, and this is pretty basic, is the approximate values for bubble rate (eg, in CEG's excellent article about using a drop checker he suggests 40 to 60b gallon 1 bubble per second, 20 to 40 gallon 1 bubble every 2 seconds, 10 to 20 gallon 1 bubble every 5 seconds).

Do these rates assume CO2 is running 24/7?, i.e. if you are using a solenoid to shut it off overnight should the rate be increased, or would this be unnecessary? I realise that the CO2 is not needed overnight, in fact is probably harmful, but should there be some compensation during the day?

Also, is there any truth in the idea that turning the CO2 up a little bit would help to drive off algae (eg by boosting the plants ability to compete?)

Thanks in advance.


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## ceg4048 (16 Sep 2008)

Hi Brian,
              It's very difficult to advise on absolute numbers of bubble rates because bubbles differ in size. If you are running CO2 24/7 then you are limited in the injection rate you can use. Shutting off the CO2 at night allows you to inject at higher rates although this does not mean that 24/7 is automatically inferior. It depends on the tank size, flow rates, lighting and so forth. Bubble rates therefore are a means to an end. So it's more accurate to say that if have livestock in the tank and if you use a solenoid then you _can_ more safely increase the injection rate compared to a 24/7 scheme.

The initial bubble rates in the dropchecker article were just standard conservative values we agreed on that would not immediately annihilate the fish just starting off. Increase the rates as the plants grow or if you see CO2 related algae. I'm always making adjustments to the injection rate due to these factors as well as because the regulator I use tends to slow the rate as the pressure in the cylinder falls. Keep an eye on the plants and they will tell you if they need more CO2. If you see indications of CO2 related algae (hair, staghorn, BBA) or if you see indications of Carbon starvation (melting, browning, disintegration, leggy growth) then increase the rate.

Try not to think of plant growth in terms of a competition between higher plants and algae. This mindset will always lead you down the wrong path. CO2 does not "drive off" algae because algae are plants too and they love CO2 as well. Higher plants cannot compete with algae for nutrients just like elephants do not compete with mice for their food. The needs of the plants are so much higher while the needs of algae are so much lower. 

An increase in CO2 availability means an increase in Carbon of which the basic structure (or building blocks) of plants are made. More structure means more growth and more health. In some ways it would be better to think of algae in the same way we think of hyenas or vultures. Algae attack when plants are unhealthy, and algae recede when plants are healthy, so increased CO2 generates healthier plants which then eliminates the conditions in which algae tend to attack.

Cheers,


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## aaronnorth (16 Sep 2008)

i dont go with the BPS etc.

For my 60l, it is recomended 1 bubble every 3 seconds, but i inject 3 BPS!

Could CO2 level be so high that it kills off the plant? I have read that CO2 above 40pppm can block the enzymes in algae and kill it.


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## ceg4048 (16 Sep 2008)

aaronnorth said:
			
		

> ..Could CO2 level be so high that it kills off the plant? I have read that CO2 above 40pppm can block the enzymes in algae and kill it.


Well I've never killed a plant using CO2 but I have killed them not using enough CO2. If it can be driven to levels toxic to plants you're more likely to kill your fauna way before that happens. Which enzymes are we talking about? Plants produce thousands of different kinds.

Scientists found that terrestrial plants vary the number of stomatal openings on their leaves as a function of the mean CO2 concentration in a given growing season. The stoma are the entry paths for gas exchange. The higher the concentration the lower the number of stomata. Fossil records have shown variability in the CO2 concentration based on the stomatal population within the leaf fossil. From what I recall, recent atmospheric CO2 concentrations have been somewhere between 280 ppm (pre-industrial age) to about 370ppm (modern day).

That's why I don't buy the 40ppm lethal dosage figure. No way, no how. Can you see why dropping plants in a tank and then feeding them a measly 20-30ppm of CO2 causes them to object violently? 

Cheers,


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## aaronnorth (17 Sep 2008)

> Well I've never killed a plant using CO2 but I have killed them not using enough CO2. If it can be driven to levels toxic to plants you're more likely to kill your fauna way before that happens. Which enzymes are we talking about? Plants produce thousands of different kinds.



I dont know, it was on a topic that George posted on TFF, might be a bit out of date from when he wrote that   

http://www.fishforums.net/content/Plant ... n-Dioxide/



> Carbon Dioxide Levels and other Water Parameters
> 
> Recommended levels of CO2 are 20 to 35ppm. It is important that these levels remain fairly constant, as fluctuating levels are known to cause algae. Higher levels are sometimes used to fight off algae ? it is known that levels higher than 40ppm can block the enzyme production in the algae cells. However one must pay attention to the behaviour of the fish as levels higher than 35ppm are known to cause health issues.


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## ceg4048 (17 Sep 2008)

Well the basic information of that article is valid but I have not seen any evidence indicating toxicity at 40 ppm. But this is the nature of science and we have a better understanding today than we did 3 years ago. Three years hence I would hope we'd have an even better understanding than we do today. 8)

If you look at Chuck Gadd's site he advocated 20 ppm CO2 and lower nutrient levels back then. The pages haven't been updated. Years before that Sears & Conlin thought limiting PO4 would limit algae. It took arguments and experiments by Barr to convince them otherwise. Years before that Dupla was still ripping people off with their Drops until Sears & Conlin figured out that you didn't need to spend £580 per liter for KNO3. 

Cheers,


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## Skatersav (28 Nov 2011)

One thing I have learnt about bubbles per minute is that the appropriate level can vary enormously depending on the type of method used to "inject" the CO2 into the water.  I was using one of those JBL spiral jobs with some success but I heard the inline diffusers were more effective so switched over.  I mistakenly did not change the BPM into the tank and stupidly went away for 24 hours.  On my return, the fish were all struggling (sitting at the bottom, panting, and ultimately swimming on their sides) and it would seem were suffering from CO2 toxicity.  I turned off the CO2, raised the spray bar above the water level (to create some surface disruption) and added in an air pump and they were all completely fine within about three minutes (which also shows just how detrimental to CO2 levels any surface disruption can be).  Moral of the story is: care is needed when you change your CO2 system and BPM as a method of determining a suitable level of CO2 injection is a relative one, not absolute, a reference rate for your tank and your set up being a requirement before you can start using it to improve performance.

I hope this lesson helps someone avoid the distressing scenes in my own tank.  Nothing died from this episode but, whilst not exactly an animal rights extremist, I don't like seeing animals suffer, especially those in my care.

Thanks, Sav.


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## GregP (10 Apr 2013)

Great read as I am new to the hobby and still learning. I wanted to use a reactor to keep equipment out of tank but keeping noise to an absolute minimum is essential. Is the increase in noise noticeable?


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## ceg4048 (10 Apr 2013)

Hi,
   No, the noise is not really noticeable unless the injection rate is very high, especially if filter(s) are running.

Cheers,


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## SUE MERCER (1 May 2013)

oh heck, looks like Im going to have to drink some coke and make myself a CO2 system. Really useful read cos as a student as I cant afford to buy everything I need straight away.


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## Misha (8 May 2013)

I have been using a pressurised system from Fluval. It's not the best and the little things run out quicker than I would like. Definitely going to try to rig up my own solution to save the cash.


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## John_42 (13 Jul 2013)

Thanks all for a great forum and good information. I like to share some info.
The pH can vary very much during 24 hours due to CO2 and photosynthesis.
I found this logg of a 180l aquarium. pH goes from 7.35 to 7.95 during daytime.


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## Ady34 (13 Jul 2013)

That seems confusing as CO2 should reduce the ph during the photoperiod not increase it. Maybe the photoperiod is backwards, or the result are from a non co2 tank, or co2 is injejcted 24/7?


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## dw1305 (15 Jul 2013)

Hi all,


Ady34 said:


> That seems confusing as CO2 should reduce the ph during the photoperiod not increase it. Maybe the photo-period is backwards, or the result are from a non co2 tank, or co2 is injejcted 24/7?


Could be either no CO2, or the level of CO2 added during the photo-period is lower than the amount used by the plants.

The graph just illustrates the changing levels of CO2 (the pH reduction is caused by the small proportion of dissolved CO2 that forms carbonic acid - H2CO3) and dissolved oxygen. Oxygen is a base (it it is really O-H in the hydroxyl ion) so as CO2/O2 ratio changes the pH varies. When the pH is at its maximum, the water is probably 100% saturated with oxygen.

In the case of the graph the variation in pH is pretty small, so the water has quite a lot of carbonate buffering (dKH). This reduces the pH swing due to the HCO3- ~ CO2 equilibrium.

These diurnal pH swings are absolutely normal in soft water, I haven't looked lately, but I would expect that the pH of my tanks would be ~pH6 just before lights on, and ~pH8 during the photo-period.

cheers Darrel


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## Ady34 (15 Jul 2013)

Yeah, it would be good to see the photoperiod times with that graph also so we could see when lights on and off are in relation to the ph increase......and to know more about the co2 injection, if there was any.
The points about water alikilinity I hadn't considered, but will rightly have an effect on the swing range. Maybe it's not as straightforward as co2 injection lowers ph, but I'd have thought in a high tech injected tank that ph would decrease even with the effect of photosynthesis? I wonder if lighting intensity and photosynthesis rate effect readings also and to what degree....most likely immeasurable due to varying factors. 
Cheerio
Ady


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## dw1305 (15 Jul 2013)

Hi all,


Ady34 said:


> and to know more about the co2 injection, if there was any.


My suspicion would be that there wasn't any added CO2.


Ady34 said:


> Maybe it's not as straightforward as co2 injection lowers ph, but I'd have thought in a high tech injected tank that ph would decrease even with the effect of photosynthesis?


Yes definitely will, the depression of pH is caused by the continually added CO2 driving the carbonate ~ CO2 equilibrium towards the CO2 side. You can thing of it a bit like a "Bouncy Castle" connected to an air compressor, if you stop the compressor the castle collapses as the internal and external air pressures equalise.The CO2 you add is like the air inside the bouncy castle, the castle remains inflated (although it is covered in kids bouncing up and down), they only have an effect when you stop adding air. Same with the oxygen from photosynthesis, it only has an effect when you stop adding CO2. So in this case you can ignore the effects of oxygen as a base, because of the high concentration of added CO2 (or more correctly the unnaturally large amount of carbonic acid it generates).

You get the reverse effect in very heavily carbonate buffered water, where you have to add a huge amount of CO2 to reduce the pH. This is how you get the CO2/dKH table (that a drop checker and bromothymol blue/4dKH solution uses), and 373ppm CO2 are required to depress the pH to pH6.2 at 18dKH.






cheers Darrel


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## Ady34 (15 Jul 2013)

So it seems that this post in relation to 'co2 in the planted aquarium' is more relevant to the diurnal reaction of ph in relation to 'oxygen production in the planted aquarium' during the photoperiod.....not to co2 or even the effect of co2 outside of the photoperiod as that levels off at ph 7.35 ish pretty consistently. Suppose it shows that co2 doesn't build up significantly in the aquarium overnight .....maybe that effect would be slightly exaggerated in lower alkalinity water due to the lack of buffering?


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## dw1305 (15 Jul 2013)

Hi all,


Ady34 said:


> Suppose it shows that co2 doesn't build up significantly in the aquarium overnight .....maybe that effect would be slightly exaggerated in lower alkalinity water due to the lack of buffering?


I'm pretty sure it is a dKH buffering effect in the graph, but without knowing the dKH you can't really interpret the pH. My experiences on other forums has shown me that unfortunately pH is a much more complex measurement than a lot of people realise.

cheers Darrel


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## ceg4048 (15 Jul 2013)

I agree with Darrel that it's very complicated, and that's why people should avoid trying to control the pH. The pH should only be monitored in order to ascertain the behavior of components in the water column.

Having said that, there is no way the pH will go up during the photoperiod. Sorry, but it's not happening. it doesn't matter how much buffering the water initially has. If you are adding CO2 and your pH is rising during the photoperiod, then your plants are in seriously deep yogurt. Check for leaks, blockages or a timer/solenoid malfunction. If this is data from a pH controller, check the software, firmware and hardware, because it's out of control. One of the few phenomena that can possibly explain the graph's behavior, if there are no component or system failures, is that some carbonate based (or otherwise soluble alkaline) hardscape is being dissolved by the carbonic acid as it dissolves, and then precipitates back out of solution when the gas goes off. Another possibility is that instead of gas being added, the carbon is supplied via liquid. Whatever the reason, the data shown on that graph is unreasonable and is NOT normal for a gas injected tank.

The characteristic of the pH depression is THE main tool used to diagnose the CO2 dissolution problems such as uncontrolled out-gassing, leaks, poor dissolution and so forth. Therefore a pH rise indicates extremely poor dissolution technique or other fault, and it wouldn't be surprising if the tank described by that pH profile chart is suffering CO2 related symptoms.

Cheers,


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## John_42 (17 Jul 2013)

Here is more info.

The dkH was 4 in the tank.
No CO2 added in any way. 
No CO2 system in this tank.

Constant circulation of water.
Light on = 13:00
Light off 22:00

I guess during the photoperiod the plants pick up CO2 from water right?
Less CO2 in water makes pH rise...


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## Ady34 (17 Jul 2013)

John_42 said:


> Here is more info.
> 
> The dkH was 4 in the tank.
> No CO2 added in any way.
> ...


Well that explains everything 
Amazing to show the immediate uptake response from the lights on at 1pm, and then subsequent response at the photoperiod end. 
Highlights the response times of the plants and the importance, especially to us who use the high tech approach with high light levels, of getting good co2 for lights on....the plants need it straight away!


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## dw1305 (17 Jul 2013)

Hi all,


John_42 said:


> I guess during the photoperiod the plants pick up CO2 from water right? Less CO2 in water makes pH rise..


 Yes that is half of it, the other half is that the water is more fully oxygenated and oxygen is a base, so that also causes the pH to rise.


Ady34 said:


> Amazing to show the immediate uptake response from the lights on at 1pm, and then subsequent response at the photoperiod end.


Pretty much as soon as the light is on the plant becomes a net oxygen exporter. If you think about the conditions for a lot of plants, they are going to grow in very patchy environments in terms of light. If you are plant on a forest floor where only occasional shafts of light reach the plants, photosynthesis needs to turn on as soon as the leaf is illuminated. If you had a lag period, by the time photosynthesis geared up, the light would have gone.

cheers Darrel


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## petr nehyba (2 Oct 2013)

Could I ask for your opinion once more please?

PH 7.5
KH 100 (after conversion x 0.056 dKH 5.6 if thats correct) 
adding CO2 from the fermentation canister ruffly 1 bubble in two sec and dosing easy carbo in liquid form daily also.

I want to get PH to 6.5 and get more CO2 into the tank. As far it seems my gravel is increasing the GH and KH. Is the only (easiest) way to get more CO2 in the tank and law the PH to change the gravel? It would be good anyway to get some good substrate for plants but if it wouldn't be necessary Id just leave it for now.

many thanks
Petr


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## petr nehyba (2 Oct 2013)

forgot to say GH 200 (dGH 11.2)

also my tap water is GH 40, PH 6.5
the gravel is puttinng all up.

thanks so much
P


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## ceg4048 (3 Oct 2013)

For the 1 millionth time, the only way to get more CO2 in a tank is to add more CO2. You cannot add CO2 by changing the KH. It's impossible

Unless there are tiny CO2 cylinders hidden in the gravel, no gravel can increase CO2 and it's a waste of time to even consider it.

In low tech tanks soil/organic substrate is often used which is not only high in nutrition and harbors bacteria which excrete CO2 as a natural byproduct of their respiration.

Cheers,


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## petr nehyba (3 Oct 2013)

thanks for coming back ceg.i appology again if missed something what has been said already.

i got not enough co2 in the tank. get more co2 in it seems like an easy task. although i have been told and now i would like to ask if thats correct. if ph7.5 all dosed gass co2 goes straigh out of the tank without affecting anything in the tank? if thats correct without getting PH down i have no co2. how to get PH down if CO doesnt stay to affect anything? lowering Gh or Kh or both? if thats the case and my gravel is increesing my Gh&Kh would that make sense to change it? 

i would appreciated if you find some energy and time for an advice as u did kindly before indeed.

also if nothing from above make sense im using fermentation canister and dosing max possible liquid carbon. how to increese co2 then? more yeast,suger or avoiding bicarbonate in the mix? 

many thanks
petr


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## ceg4048 (3 Oct 2013)

Petr,
	  CO2 is not easy, and the most difficult form of CO2 addition is the fermentation method. It's a very irregular delivery mechanism. I'm not sure where you live, but if you are in the UK it is not very difficult to find gas cylinders.

Nothing that you have been told is correct.

Adding CO2 causes the pH to fall, but making the pH fall does not add CO2.

Cheers,


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## petr nehyba (3 Oct 2013)

Good to have u on the line ceg, thanks.
I stay in Scotland. Cylinder is coming once the budget allows it for sure. any chance to get co2 up till then?

-is lowering the hardness in general going to help with getting more co2 in the water?
-more yeast, sugar or different mix in the canister at all?

many thanks for sharing your knowledge man. 

Petr


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## petr nehyba (4 Oct 2013)

have read ur tuttorial ceg,its very helpful.thanks. now i think i dont need to worry about that buffer in my tank (gravel) concerning co2 as it doesnt affect the amount of co2 at all.it keeps my PH higher for the same amount of CO2 than when my KH would be lower but for the same amount of CO2 in the tank, correct?that obviously doesnt mean i got enough co2 in the gank at the moment. as i see my plants i have not enough. good to know changing the gravel avoiding the buffer in the tank wont help. it would help to get PH lower for the same co2 level disolved if understand correct but thats it.
well great to have u here as said. still any idea how to get more co2 in with my nutrafin kit? perhaps two of them for my 60l tank? thanks once again, great stuff here!! Petr


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## ceg4048 (4 Oct 2013)

Yes adding a second nutrifin unit will be the way to go. However, if you are just waiting for funds to get a gas cylinder, it might be better to simply reduce your lighting, which also reduces your demand for CO2. You can also add carbonated mineral water at lights on if you have cheap access to plenty of it.



petr nehyba said:


> now i think i dont need to worry about that buffer in my tank (gravel) concerning co2 as it doesnt affect the amount of co2 at all.it keeps my PH higher for the same amount of CO2 than when my KH would be lower but for the same amount of CO2 in the tank, correct?


Yes, that's correct.

Cheers,


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## Jamie McGrath (11 Apr 2014)

Hello cam anyone tell me what size CO2 kit I will need for a 200L tank. I have a diy set up at the moment but im having trouble getting the drop checker to turn green , so I think a proper setup is needed now.
Any answers or suggestions will be welcomed, Thanks in advance.


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## Andy Thurston (11 Apr 2014)

Fire extinguisher setup! the biggest one you can fit in your cabinet. 
The New up inline from co2art, if it fits your filter hose, works very well but you might need a reg with adjustable pressure.


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## petn (11 Apr 2014)

Min 2kg cylinder and the rest from co2 art. Agree with big clown. If u can fit 5kg even better, may last about four months. I couldn't, will have to get second 2kg as refilling once a month for about 300l. Depends on how much co2 u l need. The less light, less co2 necessary. Diy is ok when nothing else available but really not good enough if you want to get things under control. Those post above r mine (p.n.) thanks ukaps for all support, things ok now.il try and post some picture of my co2 setup for you later on. Good luck!

Sent from my HTC One mini using Tapatalk


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## petn (11 Apr 2014)

Sent from my HTC One mini using Tapatalk


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## petn (11 Apr 2014)

Hope it works for u. Co2 art regulator,solenoid,splitter for four tanks, bubble counters,tubing. Connected straight to pumps for effective distribution within the tank.in one of my tanks I'm using the plastic diffuser from DIY nutrifin kit  hope that's helpful.Good luck!

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## Jason Blake (9 Oct 2014)

Hi,

This is just a matter of curosity and I am in noway concerned about it. I know the flow and distribution is about spot on (All plant all locations sway in the breeze) and my drop checker is very light green sometimes yellow (no livestock) But I am just wondering what is going on within the tank during the CO2 Injection period.

My CO2 goes on at 10am and my lights go on at 12 noon. The CO2 is shut of at 17:00 and the lights go off at 18:00. I use an inline diffuser.

I have noticed of late that during the first 6 hours of the CO2 cycle, the water is crystal clear no sign at of any CO2 bubbles. But without fail during the last hour of the CO2 period the water turns misty with what I am presume is CO2 bubbles. After about 15 mins of the CO2 shutting off the water returns to being crystal clear. 

I just find it strange how the first 6 hours the CO2 doesn't produce this mist and it is only in the last hour it happens. Is this because the water has reached maxium CO2 saturation? Is that possible? I am just curious to know why this happens! I don't personally like the mist but it is only there for about an hour or so, so I can live with it.

Thanks.


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## elettrone (24 Oct 2014)

beeky said:


> Nice work, cheers for that.
> 
> I'll mention here that the disadvantage of pH/KH/CO2 tables are that other acids caused by bogwood and decomposition can effect the results. The tables referred to assume carbonic acid is the only acid present. That's why drop checkers are increasing popular as the use of 4dKH water is more accurate. They can also be mis-interpreted by people summising that if they change their pH or KH it can effect how much CO2 is in the water.



Can you please elaborate?


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## brandon429 (18 Nov 2014)

Jason Blake said:


> Hi,
> 
> This is just a matter of curosity and I am in noway concerned about it. I know the flow and distribution is about spot on (All plant all locations sway in the breeze) and my drop checker is very light green sometimes yellow (no livestock) But I am just wondering what is going on within the tank during the CO2 Injection period.
> 
> ...


 

Jason I think that is oxygen saturation based o2 bubbling and not co2

I think it occurs end of light cycle for a reason, saturation above 105% but not before photosynthesis has had a chance to run for hours and spike up the dissolved o2 to the point later production emits as insoluble bubbles.


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## richard brown (18 Apr 2016)

How effective would the nutrafin method be as opposed to liquid carbon for a 64l tank with high lighting?


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