Hi guys,

several days ago i made coil denitrator from a PET bottle with about 40 ft of airilne tubing classic size used in aquariums. As i didn't find BIO balls in shop, i just filled it with FLUVAL cottonwool which should as well serve as BIO media.

I tested today the output of denitrator using Tetra test for NO3 and NO2. What i was surpriced, NO3 shows extreme high levels already first seconds after adding 3rd substance. Usually it takes longer time to get red colour, so i assume NO3 levels are very high. NO2 also shown extreme high ppm - both over the scale.

Yesterday when testing i just found little bit higher nitrites - around 0.3-0.5 ppm and nitrates were same as in main tank.
What i changed since yesterday was flow of the water going to denitrator from appr 3 drops per second to only 1 drop per 1 or 2 seconds. I did so after reading some forums where guys suggested to decrease the flow during initial phase.

I got afraid if this doesnt mean H2S present in output. Otherwise i just don't understand such high levels of nitrates in output. They supposed to be same or lower. I understand this device is still just in initial period, so i didnt expect it to reduce nitrates, but to add ?? I tryed to smell the output line, if i can detect some rotten eggs, but i didnt noticed.

I was substantially changing water now almost every day about 10%, because nitrates keep to be high (50-75 ppm). I never had problem with higher nitrites, always showin at trace levels. This is due biological filtering. I also use CO2 injection and recently i let water get more oxygentated by airpump, because fishes tend to keep on the top and 'eating' air. Sorry for my bad english.

Please help

can you add picture or drawing of the device you built so we can get a better idea of what is going on.