High CO2 and still have BBA
Hi Plant Nerds,
I work in an aquarium store and our 120g planted tank has been suffering from BBA for a while. I'm running out of ideas about what to try next.
CO2 is from a cylinder. Drop checker is consistently yellowish-green. More yellow than green. CO2 is constant 24-7.
RO water is used. I dose the full line of Flourish liquids, including Excel.
Ammonia - 0.25ppm
Nitrite - 0ppm
Nitrate - 30-40ppm
Phos - 2ppm
pH - 6.0 on API test.
kH - 0 (no color change using multiple different brands of tests)
Lighting is from 7 Ecoxotic Magenta/White Stunner strips. PAR at the bottom is 30, 60 mid, 120 top.
I've read elsewhere that there seems to be a higher prevalence for BBA in low ph/KH tanks. My next idea is to add a small amount of calcium carbonate into the canister filter to buffer the water a little higher. The charts I've seen for CO2/KH/PH indicate that a KH as low as mine might mean there's less than 30ppm CO2 dissolved in the water. Can anyone comment on the chemistry of that argument? Why would a tank with seemingly 0 carbonates be lower in dissolved CO2 than one with carbonates? Any other ideas about the cause of this BBA?
Any idea why my ammonia always measures at 0.25? It used to read higher (1ppm) on my API test when I dosed Flourish Nitrate more heavily. The tank is several years old, densely plants, has a modest amount of fish and is fed appropriately. None of the fish have ever showed signs of ammonia poisoning.