I think I just dodged a bullet.
I started up a new thing of CO2 in one of my tanks the other day. Nothing new. When I got home all my snails and fish were gasping for air at the surface. It didn't take long to figure out that the CO2 was the culprit. I instantly killed the CO2 and did a massive water change. It's been about 12 hours and the fish are acting more normal and all my levels are good now. No deaths, so I think this was my one "get out of jail free card".
I'm also experiencing a BBA bloom in my bullhead tank. Never dealt with it before. I read it's not harmful, just unsightly. So far it is only on some driftwood and some pothos roots. It's due for a rescape anyways, so I might try treating the affected stuff with some hydrogen peroxide on my day off. I wish I could throw in a clean up crew for long term maintenance, but my bullheads will eat anything that they can fit in their mouths. And in the case of our monster bullhead "Catfish Hunter", who, like the fish of the same name in Grumpier Old Men, is the size of a Buick and about as ugly, can easily swallow items as big as my thumb. So no cleanup crew.