CO2 MEASUREMENT USING A DROP CHECKER

[Mike Singh]

Very informative discussion. Can I please have some advice on moving the dropchecker around to different parts of the aquarium to check the CO2 distribution? What are the recommended locations?

 

[ceg4048]

Hello,
Put the dropchecker wherever it is most convenient to look at it. As I've mentioned many times before, the DC is a guide, and so wherever you put it, it will read the CO2 concentration level at that location, however the concentration of CO2 is different at every single point in the tank. The use of the DC is more about giving you an indication of the general trends in the tank, and it's there to help you monitor whether you are heading towards either too much gas for the fish or not enough for the plants. Observing the colors helps you to determine how much to decrease or to increase the injection rate. Somewhere between the two extremes lies an acceptable level, but ultimately it is up to you to observe the plants (and fish) and determine of each, their state of health. Therefore, do not become hypnotized by the various colors in the vial. Observe the colors and understand what information they are telling you, but do not fall into the trap of paying more attention to the DC than you do the fish and plants.

Cheers,

 

[Mike Singh]

Thanks Clive
Will take this onboard.
Mike

 

[ceg4048]

...Wait. I thought in the lights off period that many factors are involved in producing CO2... so I always had a fear that during the super long lights off period CO2 levels would rise and rise, and I would awake to see all my fish floating! (hence the "running DC down to blue" half-theory) So I take it from what to are saying that the CO2 production is not that great during lights off (in comparison to injecting at lights on)? and that the CO2 still is falling even though it is being produced at the same time? I think I remember in another post of yours that you mentioned the production of oxygen being somewhat independant of the production of CO2. So are they happening at the same time, just one outweighing the other?

Hi Jack,
Well the thing is that during the gas off time the CO2 production by plants and fish is not really comparable to the amounts that we add by gas injection. The higher partial pressure of CO2 in the water simply causes the gas to dissipate into atmosphere. This is always happening in fact. About 90% of the gas we inject dissipates immediately into atmosphere. That's why we have to inject gas for hours at a time to keep the concentration level high enough to satisfy the plants under high lighting conditions. When you turn the gas off the concentration level falls and the CO2 production from plants and animals is only a minor contribution. We don't really worry about that too much. The real problem for fish is the low Oxygen content of the water because the plants compete with the fish for Oxygen all night so that by morning the Oxygen content possibly can be too low. High CO2 concentration levels do lower the efficiency of the Oxygen carrying capacity of the blood, so that's why the combination of high CO2 and low Oxygen is a raw deal for fish, but the CO2 concentration with gas turned off drops significantly, even with the contribution of the CO2 excretion by the organisms in the tank. It's the low Oxygen that does the real damage. Oxygen does not dissolve very well in water at all. The saturation levels of Oxygen in water is perhaps 8ppm at sea level and at room temperature, and we are lucky if we can keep it at 4ppm. It's a miracle that fish can breath at all quite frankly.

I don't think I would have said that the production of these two gases were independent. During the photoperiod, the production of Oxygen by the plants depends on the amount of CO2 being fed to them + the amount of light striking them, + the amount of nutrients being fed to them, so during the photoperiod, there is a relationship between CO2 injection and Oxygen production within the plant. This then affects the amount of Oxygen being discharged into the water column by the plant tissues. At night there is no Oxygen production so the tank inhabitants have to depend on the amount of residual Oxygen left over from that days production, and when that is used up they have to depend on Oxygen being dissolved into the water from the atmosphere.

What I would have said is that the solubilities of the gases are independent. The amount of dissolved CO2 does not affect the amount of dissolved Oxygen. Each has their own solubility characteristics and are therefore independent within the water column.

So lets say during the day I inject 20ppm CO2. That value will generate a certain rate of Oxygen discharged into the water, but, both plants and animals are also consuming Oxygen at a certain rate. Some of this Oxygen also escapes the water into atmosphere at another rate. With this amount of CO2, the water column may or may not have the maximum dissolved Oygen value as a result of these factors, however, if I increase the injection rate sufficient to dissolve 30ppm or 40ppm, the Oxygen discharge rate will increase to the point where we may dissolve the maximum amount of Oxygen (8ppm or thereabouts) into the water faster than the rate at which plants, animals and microorganisms are consuming it. The water can no longer hold any more Oxygen. Most times, the rate at which the Oxygen is being discharged may be faster than the time it takes for the Oxygen molecules to dissolve, and so the molecules escape to atmosphere immediately. This is the phenomenon we observe typically when plants are pearling.

Sounds convoluted, I know, but hope it clarifies...

Cheers,

 

[jalexst]

Great.

Thanks ceg, Very informative as ever!

Aside from myths, legends, and whatever is printed in outdated books, it is the understanding that we all need. Then we can observe, come to our own conclusions and adapt what we are doing to suit.

This is why I enjoy reading your posts. Because you are teaching instead of telling.

Cheers mate,

Jack

 

[Nathaniel Whiteside]

Thanks for an amazing insight into Co2 related issues.
I like your direct approach to telling people what they require. As Jalesxst said, Your teaching skills are great.

Regards

 

[pariahrob]

My CO2 system is arriving today for my first planted tank and this thread has been a godsend in helping me understand why I should be doing what I plan to do. There are loads of threads/posts saying what to do but fewer that give the reasoning.

Thank you so much for sharing.

 

[Antipofish]

My CO2 system is arriving today for my first planted tank and this thread has been a godsend in helping me understand why I should be doing what I plan to do. There are loads of threads/posts saying what to do but fewer that give the reasoning.

Thank you so much for sharing.

Just remember, what works for one tank may be too much or too little for another. Drop checkers are useful but not definitive 🙂 What CO2 system have you gone for ?

 

[plantnoob]

excellent write up which has answered pretty much every question i had about getting your co2 right . thank you for taking the time to post this

 

[TarkMalbot]

Thanks for the great information. Lots of chemistry to get my head around in time but bringing things right back to basics I am a little puzzled by how you set up the Drop Checker with fluid and then adding water to it. I have a very basic drop checker as shown below which I just add indicator fluid to. Is this a pre mix of what you are describing throughout thie thread?

 

[scuttler]

Have to say, as an Chemistry teacher i love the application on Chemistry that a high tech fish tank brings 🙂 Some great information

 

[plantbrain]

I do not even like these things. They became popular a second time in the last 4-5 years.
Most target 30 ppm of CO2, but is 30 ppm optimal?
So can you really tell between say a pH color of 6.4 and 6.6?
Most cannot.

What the difference in CO2 there?
It's huge if you are at the higher, not so bad at the lower end of the scale.




Most of the better scapers seem to eyeball cO2, they start with some relative measure of dosing for CO2, then they tweak and adjust slowly from there.
I do the same thing with the pH/Kh chart, but not those charts above🙂
Also, as you depress the pH with CO2 gas, the concentration will increase a lot more(eg, it's non linear) for each 0.2 units of pH.
Say you have a KH of 3 degrees.
At a pH of 7.0 you would have 9 ppm
At a pH of 6.8 you would have 14.3 ppm
At a pH of 6.6 you would have 22.6 ppm
At a pH of 6.4 you would have 35.8 ppm
At a pH of 6.2 you would have 56.8 ppm
At a pH of 6.0 you would have 90 ppm

Differences between each 0.2 pH units:
5.3 ppm
8.3 ppm
13.2 ppm
21 ppm
33.2 ppm

So your pH measurement and observations need to be very good when you use more CO2. If you over do things at the higher ppm's, it only takes a little bit of change to dramatically increase the CO2.
This is one reason why many people fail when adding more CO2 and gas their fish instead. If each 0.2 pH units were only 5 ppm difference, then it would be pretty easy to adjust CO2. This is also a good reason to buy a nice CO2 regulator, needle valve etc.
Ah but what do I know, hehe:icon_mrgr
Since many use the drop checkers and there's little differences between the colors and those color changes are at best, 0.2 pH, what does this say at the higher ppm's of CO2? Not much.
Or if they use colormetric pH measure? Similar.
A good 0.01 accuracy pH meter is likely the best relative measure for CO2 using pH.
I knock my pH down about 1.4 pH units. This is about 47 ppm.
If it went to 1.6, then I'm at 75 ppm's, if I back off just a hair, 0.1 pH units, then I'm about 1.5 pH units, I'm at 59 ppm. 1.3 pH units, 38ppm, 1.2 pH units, about 30 ppm.
Tweaking CO2 is not some simple thing. It's not something to just wing it and assume the drop check has to be correct. You need to be careful.
A good pH meter can help make small tweaks and adjustments.

I'd say the chart is a better approach, as the drop checker is essentially a relative measure, but slow to respond and even harder to tell between pH.

This really becomes a much much larger issue if you add more light/more CO2.

 

[ceg4048]

Tom's absolutely right, of course, but inexperienced folks look at the charts and freak out, so
it's a much more palatable proposition to just look at colors. It's hard enough convincing people that they shouldn't worry about the ph changes. Standard test kit warnings apply!😛

I am a little puzzled by how you set up the Drop Checker with fluid and then adding water to it. I have a very basic drop checker as shown below which I just add indicator fluid to. Is this a pre mix of what you are describing throughout....

Hi,

Yes, the article is a couple years old and the premixed solutions were not common place at that time. When you follow the instructions on that kit you will end up with the identical mixture..distilled water adjusted to 4dkh with some bromothymol blue added.


Cheers,

 

[plantbrain]

Trying to get folks to test is tough, but for newer folks, the pH/KH is likely the best approach since it never under estimates the CO2 content.
In may overestimate it, so many think they have more CO2 than is actually there.
But NEVER the reverse.

The chart brings it's own set of the newbie issues. It's a learning curve and steep for some, but it's not that bad. Still, it's one of those things that needs addressed. Same with the drop checker assumptions and poor resolution. I think as you advance, the drop checker is really a worthless tool, whereas I still, even 20 + years later, still use some aspects of the pH/KH relationship.

FYI, Dupla introduced the drop checkers back in the mid 1980's here in the USA. We did not bother with them, instead opting for the pH meter + KH chart.
About 4-5 years ago, I offered some 4 degree KH reference solution and then anyone with Bromo blue could DIY the liquid.

Still, I think it's like going gold on the CO2 equipment: buy a nice gas tank set up and a pH meter. Use something that's going to offer you control you can use over the long term, even if the initial 1st step it a little tougher.
It leads to better thinking and results.

 

[plantbrain]

Problems with the pH/KH charts:

1. The color coded ranges are not correct IME
2. Many newbies think they can add other things like peat or tannins, other acids to depress the pH, and magically obtain CO2. This is not true, to get more CO2, you have to add more CO2 gas.

Simple approach to the pH/Kh chart:

Measure the KH with a good test kit, eg Lamotte Alkalinity test kit is good to about 4 ppm.
Then look at the chart and target say 30 ppm to start off with.

Then add enough CO2 to hit that point over the lighting interval.

That's it.

Now if you have growth issues and algae still, poor new growth, then you will add more CO2 gas slowly going down by 0.1 pH units per week till you see optimal new growth and fish and livestock are fine.
This is the tweaking stage.

You can adjust by eye only using a drop checker.This is more dicy for newbies and pros alike. I'd rather be able to measure it relative to the pH.
It may not be exact, but relative to a starting point, it's far more accurate than anything else we have to work with.
In several months, I'll have a device that addresses the issue and you can avoid the whole KH issue like the Drop checker does, but it'll respond in 60 seconds and will be accurate to about 1 ppm.
Should run about 50-100$ or so.

 

[TarkMalbot]

SO what your saying is test your KH and then use the chart and go across to 30ppm Co2 and see what PH that should be and then inject Co2 until you have that desired PH when the lights are on and the plants are using the Co2 the most which you test with a PH meter or Test kit?

 

[TarkMalbot]

And although I haven't checked my PH as I am away from home can I assume that because the KH of the water shouldn't have changed (or will it??) and my drop checker has gone from Blue to Green that it means the PH must have gone down?

 

[plantbrain]

SO what your saying is test your KH and then use the chart and go across to 30ppm Co2 and see what PH that should be and then inject Co2 until you have that desired PH when the lights are on and the plants are using the Co2 the most which you test with a PH meter or Test kit?

Yes.

BTW,
Aquarium KH has no effect on the drop cheker.
That is about the only real benefit to the drop checker method.

I'll have a device folks can buy in a few weeks or so that will take that benefit and the benefits of the pH meter/probe and combine them for a 60 second 99% accuracy reading.
And that's not 3000$ USD.

 

[AverageWhiteBloke]

I'll have a device folks can buy in a few weeks or so that will take that benefit and the benefits of the pH meter/probe and combine them for a 60 second 99% accuracy reading.
And that's not 3000$ USD.

Intriguing! Will be watching how this develops. Always good to read back through these stickies. I often find something I thought I understood and actually didn't 🙂 I'm considering adding an airstone on a timer to come on an hour or so after lights off until the morning now it's been highlighted about the "raw deal" the fish are getting through the lights off period. My tank is quite heavily planted and quite heavily stocked. I do have the Koralia just and so breaking the surface and causing a slight ripple to help with exchange.

Out side of Toms new invention 😱 how do you test for PH before co2 injection on a currently injected tank to eliminate other acids? I think I read it somewhere on this board but can't find it now! Would it just be a case of aerating a sample and getting a ph reading before and after to calculate how much of the acidness was actually caused by the co2?

Think I may also need to invest in a decent needle valve if anybody has any recommendations? I use a TMC V2 which is either feast or famine. This seems to be compounded by the actions of my reactor. Because the flow through the reactor creates a sucking effect it causes irregular bubble counts. I didn't have this issue with diffusers as there was some back pressure and was easier to adjust.

 

[plantbrain]

Well, it could be used on a pH controller also, so it would be independent of a KH or tap water or aquarium water interference and still be highly responsive.

Basically with a good light meter and umols, a good CO2 device will round out the big 3 factors for growing weeds in aquariums.
I've jerry rigged a few up, but I want something that's marketable and easy for a semi newbie to use.