I have a 15 gallon tank and I'm wondering how many fish I can get away with. They say an inch of fish per gallon at every pet store. The thing is, one 15 long inch fish is a lot more than 15 1 inch long fish. Does anyone have a better system for determining how many fish a tank can handle?
Hi Fishophile
IMHO, the best way to tell if you have room to add additional fish, or if you are already at the maximum carrying capacity for that tank, AT ANY GIVEN POINT IN TIME, is to look at the results of water tests done for nitrates. (Test done for ammonia and nitrites should be at 0, of course.)
If the reading is no more than about 40 ppm, (and you are doing about one good water change a week) your tank is comfortably full. If it is less, you have room for more fish, but if it's higher, you have too many fish and will have to do additional water changes or remove one or more of them.
As time goes by and your fish grow and/or reproduce, the nitrate reading will normally increase and you will have to reevaluate your situation. Perhaps you will then decide to get a larger tank or to give away some of the fish. Knowing the maximum size the fish will grow to will help you guess what you will ultimately be able to care for in the tank you have.
I would like to add, however, that while you might be able to return fish to the lfs, there are some ethical matters to consider. Moving from one water source to another is not easy on any fish and it's next owner will have to deal with any health issues it develops because of it. There is also the matter that by keeping a large fish in a small tank while it is young and small, it might become stunted and never reach its maximum size and health.
My female pearl gouramis were closer to 3" and my male was more like 4" fully grown. I never seem to see the larger strains in my area. My females were very peaceful, but the male was one of the most aggressive fish I've ever had.
Even if you have one of the smaller species of pleco, I suggest you get rid of it soon and replace it with something even smaller. A tank the size of yours would be more suited to otos (a small sucker mouth fish) than plecos.