Just when you think it's safe...
Okay, got everything stabilized and decided I had better get back on schedule for my water changes and ferts.
Did a 50% water change. Gave the bottom dwellers and amanos some sweet potato and turned off the lights.
The next morning, I woke up to dead fish.
9 out of 11 of my amano shrimp were dead, scattered all throughout the tank.
My Pelvicachromis taeniatus 'Nigerian Red' that I was going to trade in for a new male Kienke was dead.
And one of my chain loaches was dead.
I cleaned out the dead bodies and tried to figure out what went wrong.
The only thing I can come up with is CO2 poisoning (although, the living fish were not gasping at the top). My convoluted idea is that the pH was artificially dropped by the new driftwood in the tank. So when I adjusted my pH controller, I was already starting out with a lower pH than I should have.
So when I did the water change, I removed the water with the lowered pH from the wood. The new water then came in with a higher pH which the pH controller then lowered back down to the setting I was using. Only this time, the lowered pH wasn't a combination of the driftwood and CO2, but just CO2. Thus, overdosing the CO2.
I did a 50% water change making sure to add oxygen into the tank and raised the pH setting on my pH controller.
The fish have survived overnight with that, but I don't think they are all well. One of my chain loaches is very pale which is not a good sign. I'm not sure if the other fish are okay or not. When you start looking for signs of problems, everything suddenly becomes a sign.