Are you using hydroton, lava rocks? ornamental stones? I couldn't find that info in your first post. I got into trouble with the cyanobacteria, aka slime a few weeks ago. Only had that problem with lava rocks.
Since I swaped to hydroton again, added some Richy's tea and its all good to go no! No more trouble!
Since I swaped to hydroton again, added some Richy's tea and its all good to go no! No more trouble!