I have a Juwel 180 tank, all parameters are within normal limits (0 ammonia and nitrite, 5pmm nitrate), containing, Rasbora's, Cory's, 2 Alage Eaters (possibly Siamese), 2 Pearl Gouramies and, until very recently, 12 Guppies.
The thing is that over the last few weeks the Guppies have been...