My bigger pearl gourami seems to have really bad tail rot. I do not have a quarantine tank and my smaller pearl gourami is also showing signs of fin rot. The little one has a black edging to her fins. It's a 55gallon, set up since the end of April, no fish until the last weeks of august except for some snails. In it I have 2 pearl gouramis, 6 zebra danios and 5 peppered cories. I got some Fungus Guard by Tetra from the man at the LFS who said he uses it himself, remove the filter carbon and redose after 5 days. Here's a picture of the gouramis. It was just a small amount this morning but now it looks like half her tail is gone . Oh and btw the smaller gourami is a male and the big a female of almost twice his length. I have never seen any fin nipping or quarrels.