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Optimising CO2 levels in low pH/kH aquarium

kthien

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Dear TropicalFishForums community,

What is the best way to determine I am injecting ~30ppm of CO2 into my planted tank?
A lot of websites advise that this amount of CO2 is the sweet spot for plant growth as well as prevention of algae.

I have soft tap water, with the tank having a low pH of 6.4 and kH of 2 prior to CO2 injection, with a relative drop to pH 5.9-6.0 after CO2 stops.
I suppose it is also exacerbated by having ADA soil which readily lowers pH from the tap (pH 7.2, kH 2).
I have seen the table (red/green/yellow) which utilises pH and kH to determine how much of a relative drop in pH I need to achieve optimal levels however, according to the table, I have 24ppm even before CO2 is on, and 60ppm with the drop in pH. I know this to be strange as I am battling a severe case of BBA and GSA, in which I attempted the one-two punch method (hydrogen peroxide + excel) but I digress.

Another website mentioned that CO2 levels were independent of kH, and that a better goal was to aim for a decrease in pH unit of 1.0-1.2 i.e. 6.4 to 5.4. I feel this is somewhat dangerous for my tank as when I approach 5.7, my bottom dwellers (corydoras) exhibit signs of gasping and abnormal behaviour of swimming nearby the powerhead/higher areas of the tank.

Should I attempt to raise my pH and kH through external means? I believe using marble chips could work, as I'd rather reach an equilibrium with them as opposed to constantly add baking soda.
I also think there is also the possibility of poor gaseous exchange as my tank sits at pH 6.4; would residual CO2 levels be the cause? I am thinking of either running an airstone overnight or purchasing a surface skimmer.

All in all, I was hoping if anyone had any advice or thoughts on my situation, thanks.
 

Colin_T

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You can buy CO2 tests kits to monitor the levels in the water.

If your pH drops when you add CO2, there is either not enough KH or too much CO2.

You should avoid fluctuations in pH because it can kill the fish. Too much CO2 can drop the pH and cause acidosis, as well as CO2 poisoning, where the body doesn't get enough oxygen and cell damage occurs.
 

Byron

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Another website mentioned that CO2 levels were independent of kH, and that a better goal was to aim for a decrease in pH unit of 1.0-1.2 i.e. 6.4 to 5.4. I feel this is somewhat dangerous for my tank as when I approach 5.7, my bottom dwellers (corydoras) exhibit signs of gasping and abnormal behaviour of swimming nearby the powerhead/higher areas of the tank.
This behaviour is not due to the pH but to the level of oxygen/CO2. I noticed this in my Corydoras tank a few years ago, though it was not as bad as you portray. In my case, the cories were respirating much faster at the beginning of the day--"day" meaning the early morning when the tank light came on, preceded by the darkness of "night." I surmised, correctly as it turned out, that the normal increase of CO2 during darkness and parallel reduction in oxygen that occurs in a planted tank (even natural or low-tech like mine) was affecting their uptake of oxygen. I increased the surface disturbance 24/7 and never saw this again. The pH in some of my tanks is well below 5, and in the cory tank I believe it is in the low 5's.

I do not worry over "buffering" pH with KH. If you have soft water fish species, it is better to ensure you provide them with soft water (a low GH) and let the pH do what it wants; it will stabilize and remain steady according to the biological system. Provided the fish species are suited, there will be no problem.

Adding diffused CO2 is always a risk, and there is now evidence that it does impact fish long-term. Planted tanks is a rather involved topic, but CO2 is more abundant naturally in a tank with fish than you might think. And while it is true that CO2 can govern plant growth, so too do all the other nutrients which the plants require. It is all a question of balance between light and nutrients.
 
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kthien

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You can buy CO2 tests kits to monitor the levels in the water.
Thanks Colin. What test kit do you personally use? Would something like this work?

This behaviour is not due to the pH but to the level of oxygen/CO2. I noticed this in my Corydoras tank a few years ago, though it was not as bad as you portray. In my case, the cories were respirating much faster at the beginning of the day--"day" meaning the early morning when the tank light came on, preceded by the darkness of "night." I surmised, correctly as it turned out, that the normal increase of CO2 during darkness and parallel reduction in oxygen that occurs in a planted tank (even natural or low-tech like mine) was affecting their uptake of oxygen. I increased the surface disturbance 24/7 and never saw this again. The pH in some of my tanks is well below 5, and in the cory tank I believe it is in the low 5's.
Thank you Byron, I understand. May I please ask how you increased disturbance? I have purchased a skimmer/lily pipe inflow, but it seems with the Corona pandemic, processing and transit times have been affected. Do you also prescribe to the notion of 30ppm being a reduction of ~1.0-1.2 pH drop? I've had some partial success in eliminating BBA through symptomatic treatment but would really like to get to the underlying problem.
 

Colin_T

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The CO2 test kit in the link is probably fine. I would have just asked the local pet shop to see what they can get in, and check the expiry date on it because CO2 test kits don't sell very often and can expire while sitting on the shelf.
 

Byron

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Thank you Byron, I understand. May I please ask how you increased disturbance? I have purchased a skimmer/lily pipe inflow, but it seems with the Corona pandemic, processing and transit times have been affected. Do you also prescribe to the notion of 30ppm being a reduction of ~1.0-1.2 pH drop? I've had some partial success in eliminating BBA through symptomatic treatment but would really like to get to the underlying problem.
It has been several years since I read anything about the CO2/pH issue and it is something I have never had to worry about or deal with as I have low-tech (natural method) planted tanks and once I can assess the CO2 reduction from primarily problem algae (yes or no) I balance the light duration accordingly and all's well. The natural CO2 produced in an aquarium stocked with even a moderate number of fish is more than many realize. I have never added CO2.

As for surface distyurbance, the filter return is the easiest method to achieve this. You just want to have some rippling of the surface water at one end. I did this by adjusting the filter return spigot (removing the spray bar so the water was a stronger concentrated flow) on my larger tanks (4 feet and 5 feet length) to aim directly into the end wall on one side, which created quite a ripple for about 1/4 of the tank surface. In smaller tanks I use an internal power filter which is basically just a motor and sponge material, and the filter return can be adjusted to produce more roughness at the rear corner where the filter is hanging. My cories and loaches (separate tanks) seem to really appreciate this.

BBA like all problem algae is due to an imbalance of light and nutrients. I have gone through this several times. Light intensity is the major factor, and if this is the correct spectrum for plants you can ensure there are sufficient nutrients in balance, and adjust the duration of the light. Every aquarium is different biologically, but in my case with the moderate (some wold call it low I expect) light I use, balancing that with minimal supplements (comprehensive fertilizers) and then tweaking the duration down to seven hours daily, I solved the algae issues and for several years now have had none.
 
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kthien

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BBA like all problem algae is due to an imbalance of light and nutrients. I have gone through this several times. Light intensity is the major factor, and if this is the correct spectrum for plants you can ensure there are sufficient nutrients in balance, and adjust the duration of the light. Every aquarium is different biologically, but in my case with the moderate (some wold call it low I expect) light I use, balancing that with minimal supplements (comprehensive fertilizers) and then tweaking the duration down to seven hours daily, I solved the algae issues and for several years now have had none.
I agree, I do think it is due to my new lighting fixture, it is far too strong and I've got a small dimmer unit on its way but again, transit times aren't too great right now. Rather, I've since suspended it higher above using adjustable retractors with counterweights hung from my ceiling - the ones used for hydroponics - and after coupling it with the diffuse peroxide/glutaraldehyde treatment, algae issues have seemed to improved, at least there is no new growth and existing BBA has either withered or stagnated. I've encountered BBA once before in a low-tech tank and it was truly a bane so this time round I am keeping on top of my maintenance. Hopefully I can beat it.
 
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