The fundamental question perhaps is, do low oxygen levels help pathogenic Myobacteria to flourish?
No problem with the impeller or blue-green algae.
The canister filter is over-sized for this tank though, by a factor of about... 10 or 15, as it's a fluval 305. The hope is that it would readily mineralize any organics in the water, and as a byproduct would be pumping out a steady supply of CO2 as well.
That was the idea anyway, but perhaps something is out of balance there, or perhaps it's just some other type of disease which has nothing to do with the lights/plants/filtration.
However, my tank is low-light so maybe the plants aren't even producing a sufficient amount of oxygen. And as the fluval edge has restricted surface area, that obviously doesn't help either.
With all the talk of covering up tanks tightly to reduce co2 off-gassing I wasn't too worried about my oxygen levels initially. And when I tested the levels, I did have high oxygen levels or low oxygen levels, possibly something in-between. To tell you the truth the bloody test kit's results were useless and impossible to read...