Then you are overfeeding them and or you've never allowed the biological filter to become established. I have 50, yes 50 in a 25 gallon tank / coffee table and I have no problems at all. Just regular 25% monthly water changes.
Pal, if you have to worry about priming a bio-filter to keep those incontinent little scavengers from turning the water into a baby diaper, you need to find a different fish. LOL I like my gouramis, thank you very much. My under-gravel plate and the associated bacteria bed beneath work quite well together to help the main filter keep the water clear.
