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Old 02-13-2005, 10:57 PM   #1 (permalink)
Join Date: Feb 2005
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cheeboonyong is a regular member
Default BBA and CO2: how much CO2 is enough?

Hi everyone,

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.

Boon Yong
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