CO2 In the planted Aquarium

[aaronnorth]

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I dont know, it was on a topic that George posted on TFF, might be a bit out of date from when he wrote that 😉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

 

[ceg4048]

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,

 

[Skatersav]

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.

 

[GregP]

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?

 

[ceg4048]

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

Cheers,

 

[SUE MERCER]

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.

 

[Misha]

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.

 

[John_42]

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.

 

[Ady34]

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?

 

[dw1305]

Hi all,

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

 

[Ady34]

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

 

[dw1305]

Hi all,

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

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

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

 

[Ady34]

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?

 

[dw1305]

Hi all,

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

 

[ceg4048]

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,

 

[John_42]

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...

 

[Ady34]

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...

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!

 

[dw1305]

Hi all,

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.

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

 

[petr nehyba]

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

 

[petr nehyba]

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