Constipated fish-I think

Question
We have a 55 gallon tank with 3 mollies, 3 adult platys, an unsidedown catfish, 2 mystery snails and about 20 or so baby platys.  Several of the fish have swollen bellies and long tailing poops.  We feed some flakes, tube worms, or brine shrimp trying to vary the feedings.  I think the fish are constipated since the mollies are all female and have been in the tank for at least 6 months.  The platys could be making more babies, but a few of the larger babies also have the tailing poops.  I read that constipation can be treated with magnesium sulfate (epson salt) but also read that you shouldn't add any type of salt to a tank with catfish.  I am hesitant to try fasting the fish since we want to keep a few on the platy babies and I am not sure what fasting would do to them.  Any advice?
Ann

Answer
Hi Ann
A lot of the catfish species are salt sensitive, not sure on the upside down catfish though.  Here's their scientific name Synodontis Nigriventris you can try searching around to find out.  

For the constipation, try feeding a pea to the fish.  You can use any kind, I use the unsalted canned, just easier for me, but frozen then thawed is fine as well.  I break open the shell, and feed the inside of the pea.  I don't know any fish that will turn that down.  Feed only the pea for a few days and see if that helps.  Then incorporate the pea into their diet at least once or twice a week with the other stuff.

Also what you can do with the babies/fry, if they're still fairly small, you can put them into a breeders net-just hooks onto the side of the tank.  That way you can still feed them the normal food and feed the others the peas.

Hope that helps and good luck!

Christy