robin

I have a 5gal tank and have had a f blk. molly in it for about 3mos. 3wks ago I added a m and f. They are all now clamped fins and bouncing off of things. What is going on? pet store is quessing. I have not tested the water. The 2 platies and plecostoma are doing fine . Thaks R

angelfish220

All that in a 5 gallon

You want to know how big a pleco gets? 20 inches long

They are probably like that from nitrate poisening or they dont have enough space.

sirdarksol

Welcome to Fishlore.
I'd be willing to bet that overstocking is your issue. A 5g tank isn't really even big enough for a full-grown molly. They like a lot of vertical swimming space. Aside from that, the general guideline is 1" of fully-grown fish per gallon of tank. A common pleco grows to be 18" and produces far more waste than a normal fish of its size, so that one alone overloads the tank. This would likely have happened eventually, adding the two mollies just catalyzed things.

COBettaCouple

Welcome to Fishlore.

Unfortunately, that tank is extremely overstocked and it's pretty certain that your water chemistry is toxic to the fish. The guideline is 1" (adult size) of fish per gallon so a larger tank would be a real need for them. I would recommend Prime to treat the water and daily water changes of 35-50%.