I set up a betta sorority with 9 females last fall in a heavily planted filtered 40 gallon aquarium. The tank water parameters are 0/0/20ppm, and I perform a 25% water change every 2-3 weeks. A pecking order was established and the tank was in harmony for 6-7 months. I had to move the tank to a new house a few months ago, and it has been a slow death spiral since. The bettas we put into jars and 80% of the after was taken out of the tank for the move, which overall took a few hours since I wasn't moving far. After filling the tank back up with clean water, I reintroduced them back in, and every month has had its issues.

The first betta became blind shortly after the move, which I could tell by the way she couldn't recognize food in front of her or other bettas surrounding her. Eventually she stopped eating and died shortly after. The next month, one developed gill hyperplasia which caused one of her fins to become inflamed and stick out. Epsom salt did well to reduce the swelling the first time I treated it, but it did not stop it after it came back again more quickly than before, ultimately taking her life. This time around, I am confronted with a betta developing dropsy of all things. I'm debating the risk/rewards of treating her with epsom salt and anti bacterial medicine or euthanizing with clove oil.

There seems to be an unforeseen plague of bacteria in the water causing these illnesses, as I'm confident the water is clean otherwise. By process of elimination, I'm coming to terms that maybe it is the driftwood I have placed within the tank. This piece was recovered from Lake Erie, which was already a risky move in my opinion. I did everything I could that was recommended for using natural driftwood:

I first kept it in the freezer for 3 days. Then, I let it soak in chlorinated water for 2 weeks, making sure to periodically take it out, scrub, and put it back into new chlorinated water. Lastly, I ran it through the dishwasher (after running a cycle to clean out soap residue) twice back to back on two occasions.

Even after all of this, I'm still paranoid given how thick it is and where it came from. Maybe it isn't the reason my fish are getting bacterial infections, but at this point I'm considering removing it to rule it out completely even though I don't really want to.

Am I thinking about this the right/wrong way? Are there other reasons I am not seeing that could cause a varied degree of bacterial diseases even within relatively clean water?

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