BBA and CO2: how much CO2 is enough?
I'm new to APC. I've been keeping planted tanks for close to 2 years now and I live in the sunny country of Singapore.
Recently, I changed my 4x2x2 ft (about 400 litres) tank to a low-maintenance tank setup due to time constraints from my job and new baby. I've had a very serious outbreak of BBA since and I'm not too sure of the reasons. I've also looked through some of the previous posts here and it seems like Tom Barr's opinion is that adequate CO2 will beat BBA, keeping it from reproducing (although adult BBA still needs to be manually removed).
My current situation:
1. My pH is about 6.6 before the photo-period (I switch my CO2 on about 1 hour before lights on)
2. My pH just after lights come on is 6.3
3. My pH just before lights go off is 6.2 (CO2 is switched off together with the lights. Duration of lights is 9 hours)
I measure my pH using a pH pen, so it should be accurate enough to 0.1.
4. My carbonate hardness is 3-4
5. 2x54W of T5 (high output) lights. I have mostly crypts, anubias, moss as the main plants, so the low amount of lights seems adequate.
6. I add about 3-5 ppm NO3 twice weekly (from Potassium Nitrate), <1 ppm PO4 weekly (from Potassium Phosphate, I add 4-5 crystals) and 20 ml of Tropica Mastergrow weekly.
7. I change my water about 40% weekly.
Seems like my CO2, based on pH of 6.2 to 6.3 and 3-4 dK should be about 45 to 75 ppm.
I'm dissolving my CO2 using a pressurised system with a Dennerle Cyclone 5000 with a dedicated power head. I believe this should give good diffusion rates.
However, I suspect there may be some other unknown acids which are misleading the pH readings. I am using ADA aquasoil, which is a peat-based gravel, so it does lower the pH. Having said that though, the gravel is 2 years old, so probably most of the peat should have been exhausted. I also have quite a fair bit of driftwood which may leak tannic acid (?) into the water.
So my problem is that I don't really know what is the true level of CO2 that I have in my tank. So far, the fish are not suffering from CO2 poisoning yet.
Given that I have this unknown acid problem in my tank, how do I know for sure that my CO2 is adequate? I believe many other people also use driftwood, so my situation shouldn't be unique. What is the typical ambient level of CO2 that I should be expecting without CO2 injection and can I make deductions from there? For instance, at dK 4 and ambient CO2 of say 10 ppm, my pH should be about 7 but my actual pH is actually 6.6. So should I aim for 6.0 pH instead of 6.2?
Thanks for reading this very lengthy post.
Hi Boon Yong,
If I read correctly, your tank is ~400L with only 108W, > 1 WPG.
This is really a low light tank. For low light tank, you usually don't have to worry abount CO2 level. Many low light tank don't even inject CO2.
Tom Barr's opinion that high CO2 level helps to elimiate BBA usually refers to high-tech tank. It should not be necessary to maintain high level of CO2 in a low light tank.
I am not sure whether it could be due to your dosing as you seems to be dosing quite a lot of NO3 for a low light tank with mostly crypts,anubia and moss. You did not mention the fish population and feeding pattern. Low tech tank may not even require dosing of nutrients if the fishes are well fed.
So with little light to start off with, maybe I don't need so much CO2 since the rate of photosynthesis will slow down. But I still do not understand how to prevent BBA from spreading.
So in low light tanks, it's not really necessary to inject CO2 but that in turn encourages BBA growth since CO2 is inadequate? I don't quite understand it. How does the low-tech aquarium concept by Diana Walstad overcome this problem?
My fish load is fairly high, about 150 tetras in all. I feed them tetrabits on a daily basis, either once or twice, depending.
Does the 2x54w gives you a good spread of light over your tank? The BBA issue doesn't seem too related to the CO2 but rather growth issues. When plants stop growing for some reason for so, they make good substrates for algae. Try trimming the Aponogeton and allowing more light to get to the plants (low light but not too low till everything stops growing...avoid shading as you do not have much light left.). Go in and remove as much BBA as possible. Try adding 7ppm of NO3, 1ppm of PO4 and 20ml of TMG right after the water change. Add more current to the tank/reactor and mix the output of the CO2 reactor good by adding some current to the output flow. Having 30ppm of CO2 is not that critical at low light level tanks but that will make sure that your tanks are never limited.
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