DIY CO2 questions

[PerfectDepth]

I'm in the planning stage for a 20 long build with DIY CO2, and I'm wondering about whether or not I'll need to run aeration at night.

For lighting, I have a 30" Beamswork LED: 6500K, 57 X 0.5 watt LEDs (26W total)

Fish stocking plan:

8 harlequin rasboras
10 neon tetras
5 forktail blue-eye rainbowfish (p. furcatus)
3 or 4 otocinclus
RCS and ramshorn snails

...not overstocked, but a fairly heavy fish load. I'm kinda worried about the oxygen level possibly dropping too low at night. Should I run an airstone on a timer at night just to be safe? I have moderately hard water that is very well-buffered straight out of the tap. I don't know the KH since I haven't even bothered testing it for several years. GH stays between 130 & 150 mg/L according to the water quality data on the water works' website, and KH should be fairly close to that (plenty of CaCO3 and MgCO3 in our water). pH is quite high straight from the tap, but settles to around 7.6 - 7.8.

Questions:

1.) to aerate during lights-out or not?

2.) I've never used a drop checker before.. could someone explain the importance of using a reference solution in a drop checker? I don't think there will be much risk of adding too much CO2, so would using tank water instead give me a "close enough" reading?

3.) To diffuse the CO2, I thought about placing a small airstone inside a sponge that will hopefully trap some of the bubbles, and place this diffuser behind a small powerhead for dispersion. Thoughts on this method? Will the airstone create too much back-pressure for a DIY setup?

4.) any other advice or considerations I might be overlooking?

 

[Fishfur]

Airstones won't be backed up by this amount of pressure, but they won't break up bubbles small enough for them to be absorbed into the water before they hit the surface and gas out. The sponge won't either, and if you have it that high up in the water column you will lose most of the gas to the surface. You need extremely fine bubbles with a prolonged contact with the water to get good absorption of the gas.

Surface agitation of the water also increases gassing off in general, so if you're adding C02, having a quiet surface is best. So no waterfalls of returning water, for example. Depends on the filter you're using.

A drop checker needs the reference solution because that's how it works. The solution changes colour depending on the level of C02, giving you a fast, easy, visual reading of the levels. It has to be replaced periodically because it eventually wears out, so to speak.

DIY C02 diffuser ideas are out there. I've seen folks use the end of a disposable chopstick, inserted in the end of the air hose, or wooden air stones, [ old fashioned but still made], because the wood pores make very fine bubbles. You want them coming from the very bottom of the tank, so they have maximum time in contact with water. Most commercial diffusers need more pressure than a DIY bottle can muster, so they usually won't work.

Inline diffusion is said to be the best way, by many people. If you have a canister filter, you can do inline. Some feed the gas to the filter impeller, to chop up the bubbles. It can help, but usually causes premature wear on the impeller too.

Silicone air hose lasts longer with C02, but any air hose works. None of them last indefinitely.

Tanks experience a drop in pH when C02 is running. But if heavily planted, the plants give off oxygen during their respiration, so there's no definitive answer I know of to the question of whether aeration is needed when lights are out. Some do it simply to be on the safe side, some don't bother. Try checking the readings during day & night and see if the difference is enough to worry you. If yes, use an airstone.

It IS possible to add too much C02, and if you do, fish may suffocate. But I believe this more often happens with too much pressurized gas from a tank, rather than the DIY bottles, which don't produce so much pressure. Another reason to have a drop checker.

 

[PerfectDepth]

Airstones won't be backed up by this amount of pressure, but they won't break up bubbles small enough for them to be absorbed into the water before they hit the surface and gas out. The sponge won't either, and if you have it that high up in the water column you will lose most of the gas to the surface. You need extremely fine bubbles with a prolonged contact with the water to get good absorption of the gas.

Surface agitation of the water also increases gassing off in general, so if you're adding C02, having a quiet surface is best. So no waterfalls of returning water, for example. Depends on the filter you're using.

A drop checker needs the reference solution because that's how it works. The solution changes colour depending on the level of C02, giving you a fast, easy, visual reading of the levels. It has to be replaced periodically because it eventually wears out, so to speak.

DIY C02 diffuser ideas are out there. I've seen folks use the end of a disposable chopstick, inserted in the end of the air hose, or wooden air stones, [ old fashioned but still made], because the wood pores make very fine bubbles. You want them coming from the very bottom of the tank, so they have maximum time in contact with water. Most commercial diffusers need more pressure than a DIY bottle can muster, so they usually won't work.

Inline diffusion is said to be the best way, by many people. If you have a canister filter, you can do inline. Some feed the gas to the filter impeller, to chop up the bubbles. It can help, but usually causes premature wear on the impeller too.

Silicone air hose lasts longer with C02, but any air hose works. None of them last indefinitely.

Tanks experience a drop in pH when C02 is running. But if heavily planted, the plants give off oxygen during their respiration, so there's no definitive answer I know of to the question of whether aeration is needed when lights are out. Some do it simply to be on the safe side, some don't bother. Try checking the readings during day & night and see if the difference is enough to worry you. If yes, use an airstone.

It IS possible to add too much C02, and if you do, fish may suffocate. But I believe this more often happens with too much pressurized gas from a tank, rather than the DIY bottles, which don't produce so much pressure. Another reason to have a drop checker.

Thanks! Just to clarify, I know the sponge won't necessarily break it up into smaller bubbles, I'm just hoping it will trap them and keep them in contact with the water for a longer period of time. I'm thinking this might compensate a bit for the fact that the bubbles coming from the airstone are not as fine as they should be. Once the bubbles escape the sponge, they would go through the powerhead which will hopefully further break them up into finer bubbles and disperse the CO2 enriched water through the tank. (similar to feeding it to the filter impeller) A DIY reactor would be more efficient, but I'm hoping to get away with something simpler so I don't have to run another pump, and I don't mind if some CO2 is wasted.

I'm referring to the 4KH reference solution, not the indicator solution. Some people just use tank water in place of the reference solution, and I'm wondering what the differences/drawbacks are. Though I haven't checked, I'm assuming my tank water is somewhere around 8 KH. By using tank water, you're really just monitoring pH, right? I'm thinking I can watch the pH to get an approximation of the CO2 level. Will this be accurate enough?

Thanks again for your reply.

 

[Fishfur]

If I understand what you're asking, I suspect you don't understand how a drop checker works. It's not simply a measure of pH. It allows you to use the pH at any given time to see directly how much C02 is in the water. Short answer is, if you only use tank water in a drop checker instead of a reference solution, the drop checker does not function at all. This link explains it much better than I can.

~Explanation of how a drop checker works~

The sponge might hold onto the C02 for a bit of time, but I sincerely doubt it would be long enough for significant gas exchange to take place. Once the bubble begins to rise, virtually no exchange happens until it hits the surface and is gone into the air.

 

[PerfectDepth]

Thanks for the link, but it's not what I'm looking for. Hmm.. I'll rephrase..

Basically what I'm asking is if there's any reason I can't use the drop checker to try to lower by, let's say, half a point, or maybe just down to 7.4 and then adjust from there going by pH without worrying about exact ppm. Btw I'm not shooting for 30 ppm.. I don't think so anyway. Of course it won't be green, and I could also use a liquid ph test to verify what color it should be.

Reference solution seems ridiculously expensive for what it is (water lol), and I'd rather not have to make it myself if it won't be necessary.

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[aqua_chem]

I'm referring to the 4KH reference solution, not the indicator solution. Some people just use tank water in place of the reference solution, and I'm wondering what the differences/drawbacks are. Though I haven't checked, I'm assuming my tank water is somewhere around 8 KH. By using tank water, you're really just monitoring pH, right? I'm thinking I can watch the pH to get an approximation of the CO2 level. Will this be accurate enough?

'Some peope' are just doing it wrong, that's all. The way the drop checker system works is that we know that certain concentrations of CO2 in a tank react predictably with 4 dKH solution such that we can tell the concentration of CO2 based on the pH of the drop checker solution. The mathematics only work out well if there is only pure water with 4 dKH hardness. You absolutely cannot use tank or tap water because it likely contains other acids/bases/buffers that would screw up the mathematics, making it completely unreliable as a measure of CO2.

The 4 dKH solution can be gotten for very cheap on ebay or made if you have the right tools.

 

[PerfectDepth]

'Some peope' are just doing it wrong, that's all. The way the drop checker system works is that we know that certain concentrations of CO2 in a tank react predictably with 4 dKH solution such that we can tell the concentration of CO2 based on the pH of the drop checker solution. The mathematics only work out well if there is only pure water with 4 dKH hardness. You absolutely cannot use tank or tap water because it likely contains other acids/bases/buffers that would screw up the mathematics, making it completely unreliable as a measure of CO2.



The 4 dKH solution can be gotten for very cheap on ebay or made if you have the right tools.

Thanks, this is what I didn't quite understand. That helps a lot.

Just to be clear though, will the indicator solution at least give me an accurate pH of my tank water, or not?

I've used an automatic pressurized system with a pH controller before, so let's just say I'm not really concerned with exact CO2 concentration, just pH. Will it work or not?


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[aqua_chem]

Yes, the indicator used in drop checkers is the same as the 'low pH' testing solution, bromophenol blue. It can be used as a pH indicator if you don't have a testing kit handy.


Regarding the pH, it's an inferior way to measure CO2 vs a drop checker. Measuring pH along can easily be swayed by things like wood in a tank, some substrates, or stocking levels past moderate. I would still have a drop checker available for this reason.

 

[PerfectDepth]

Thanks for your help. Ok, more specifically (just to be sure), since I do have a pH kit, will it work as a constant indicator inside a glass bulb drop checker inside the tank? (Of course changing the water and solution as needed)

Do you suppose there's any danger in dropping only half a point or less? Is there any data on the highest possible CO2 concentration at a given pH & KH value?

Edit:
Wait a sec, never mind.. are you talking about swaying of baseline pH?

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[PerfectDepth]

For what it's worth, I have driftwood and a fairly heavy stock in my current low-light tank, and my pH is rock steady. It doesn't sway any more than maybe a tenth of a point from the pH of the aged tap water.


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[aqua_chem]

Thanks for your help. Ok, more specifically (just to be sure), since I do have a pH kit, will it work as a constant indicator inside a glass bulb drop checker inside the tank? (Of course changing the water and solution as needed)

Ok, so you're asking if you can just put a couple of drops of indicator in the drop checker, and set it and forget it? If so, then yes. I rarely change my drop checker solution (as in, 4 dKH + indicator). It's good for a long time.

Do you suppose there's any danger in dropping only half a point or less? Is there any data on the highest possible CO2 concentration at a given pH & KH value?

Depends on your KH, but I would think that would be fairly mild levels of CO2 and no particular danger. As far as highest possible CO2 level, it's less limited by the physics of the tank and more by the inhabitants. Above about 50 ppm of CO2, you start seeing effects of CO2 on fish. Above about 70 ppm, you start getting into dangerous territory.

Wait a sec, never mind.. are you talking about swaying of baseline pH?

What I mean is that both the pH/KH/CO2 charts and the drop checker use mathematics that assume that carbonates (CO2, HCO3-, and CO3--) are the only chemicals in the tank. Anything else, such as tannics or fish waste byproducts throws the calculations off such that we can't say with any degree of confidence XXX color = YYY CO2 level (drop checker) or XXX pH in YYY KH = ZZZ CO2 level (charts). It sways the calculations more so than the pH really.

 

[PerfectDepth]

Thanks so much, aquachem.

I've been reading up on drop checkers and CO2 charts, and I'm understanding it much better now.

Since overall tank KH isn't necessarily entirely carbonates, wouldn't the calculations always err on the safe side? i.e. if you use a chart to look up your CO2 level using the tank's KH and pH, wouldn't it always show a higher amount than the actual concentration, with the difference being dependent on what percentage of KH is actually true carbonate hardness?

For example, when I was using a ph controller & solenoid and just assumed I was around 30 ppm.. it's likely the actual concentration was less than 30 ppm. Is it also possible it was greater than 30 ppm? I wouldn't think so, but I could be wrong. I never had any problems.

 

[aqua_chem]

Since overall tank KH isn't necessarily entirely carbonates....

By definition, KH is carbonates. The entire buffering capacity might not be carbonates though, which is what I think you mean.

...wouldn't the calculations always err on the safe side? i.e. if you use a chart to look up your CO2 level using the tank's KH and pH, wouldn't it always show a higher amount than the actual concentration, with the difference being dependent on what percentage of KH is actually true carbonate hardness?

For example, when I was using a ph controller & solenoid and just assumed I was around 30 ppm.. it's likely the actual concentration was less than 30 ppm. Is it also possible it was greater than 30 ppm? I wouldn't think so, but I could be wrong. I never had any problems.

Your water might be buffered more than your KH would lead you to believe, but there might be other acids/bases in the tank that would throw off the calculations beyond just the buffers. The calculations also assume that CO2/Carbonic acid is the only acid present in solution as well. It can go either direction, but I would say that it would probably tend to underestimate CO2 levels.

 

[PerfectDepth]

By definition, KH is carbonates. The entire buffering capacity might not be carbonates though, which is what I think you mean.





Your water might be buffered more than your KH would lead you to believe, but there might be other acids/bases in the tank that would throw off the calculations beyond just the buffers. The calculations also assume that CO2/Carbonic acid is the only acid present in solution as well. It can go either direction, but I would say that it would probably tend to underestimate CO2 levels.

Right, what I meant was that the common liquid KH tests are actually testing total alkalinity, not just carbonate hardness, and there could be a couple degrees difference. Is this true? If your calculation is based on a false KH value, the error would always be on the safe side.

So as long as these variables remain fairly consistent within the tank, or within an acceptable range of fluctuation, could pH still be at least a good relative measure of CO2 at lower concentrations? (Adjusting by tenths a of a pH point, not exact ppm, as appropriate in order to "eyeball" where it should be) I realize that at higher concentrations this would be tricky since even dropping just one-tenth a of a point could be a drastic increase in CO2.

Thanks for explaining all of this. I have a much better grasp now.


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