Water is fine. No nitrite, PH at 7.5, no other problems.
The fish are about a month old but the tank is about 4 months old and not had any previous problems.
There are 4 barbs, 4 harlequin rasbora, 4 glass catfish, 4 khuli loaches, 4 clown loaches, 2 banded garas and a siamese algae eater.
The...