The other day, I got a betta from Pet Supplies Plus, who had just received a bad batch of bettas (which both they and I were unaware of at that time). I noticed a small lesion on his side, but I didn't think much of it, thinking that it looked like the cancer lesion one of my previous bettas had had, which hadn't affected him much in his youth. But it turned out to be something much worse. Within 24 hours (by the next evening), he was absolutely covered
with what I believe to be cotton fin fungus. I immediately isolated him and asked the people at PSP for advice the next morning (today), and they treated him with everything they thought might work, then graciously allowed me to take him home, as I wanted to be there for him no matter what happened. Sadly, this afternoon, little Blue Jeans the betta died, as the fungus was just far too advanced to save him.
However, I'm now worried about what to do now with my tank. Blue Jeans was in the tank for about 24 hours, which means the fungus has been in the water. I have a little baby bristlenose pleco in the tank, so small that he's only about an inch long, and I'm really concerned about him potentially contracting the fungus since he's so small. The people at PSP suggested doing a 100% water change, rinsing the rocks and tank ornaments, and replacing all the filter media, but I'm worried that such drastic measures would be a shock to the little guy's system. But I'm also worried that if I don't do that, I won't be able to put another betta in once I find one I like, since I wouldn't want the new betta to contract the fungus either.
What measures can I take to try and eliminate any traces of the fungus from the tank? I'm really concerned about it being present.
(I have a 5.5 gal
tank with an AquaClear Power Filter, 4 anubias plants, and a moss ball, in addition to the bristlenose pleco.)