^ the brown slime. that brown mucus like looking substance that grow and then eats your plant roots.. thus sufficating your plants. Its not a mold or a fungus or alage. It belongs to a group called "micro-algae". It can switch methods for energy production and therefore does not require light. It is also unaffected by all but the strongest disinfectants. zone and h2o2 will do nothing to it. Physian 20 will eliminate it but since its in your water supply, it comes right back.
Nasty shit but using EWC tea will hold it at bay. In my case, I guess its the price I pay for municipal water that is barely disenfected and very tasty.. but has cyanobacteria in it.
At any rate. .thanks for the question as it spurred a whole new round of research on this little bastards that plauges so many hydro growers. I did however just stumble upon a possible cure. The borad spectrum anti-biotic used in aquariums.. eurthromyicin.