I have a 30x30x60 tank that has been set up for approx 18 months with clown loaches, neons, zebra danios, gouramis and catfish, but just recently have had a spate of sudden and unexplained funerals down the toilet!! I think it started a couple of months ago when one of our pair of Gouramis died, and we replaced it with a couple of others, but unfortunately they were bullied to death. We took the "bully" back to the shop and tried with another pair, but they also took to bullying, and so did their replacements, and after another spate of murders we took those back too. We have during this time also tried adding other new fish such as angels, platties and mollies - just a couple at a time - but these died without any visible signs of disease just days after being introduced to the tank. The only symptoms I noticed were that they become lethargic or swam awkwardly and seemed to gasp for air. We also lost one of the clown loaches, a couple of neons and a zebra. One day they are fine and the next I'm scooping them off the bottom. I change the water weekly, and have checked that the chemicals are all OK, with the exception of the phosphates being a little high. To combat this I have added new live plants and 2 anti-phosphate "t-bags", and also change the water every other day by 10%. The deceased danio zebra looked as though he may have had red gills so we tried a course of anti-biotics, but the deaths continue........please help.