Mickey Mouse Platy w/ messed up tail

Question
Ok ... Tank set up 5 weeks; 55 gallons

Fish: 3 red platys(Females), 2 blue platys (1 M/1 F), 2 Mickey Mouse Platys (F), 2 Dalmatian Mollies (1 m/ 1 f), 2 creamsickle Mollies (1 m/ 1F), 6 neon tetras, 2 silver Mollies (Females), 2 glofish, 3 plecos (due to autistic son WAAAAY overfeeding fishies) + 8 platy fry in breeder net (2-3 days old) - total = 32

Filter: running 2 Aqua-tech power filters

pH 7.0/Ammonia less than .25 ppm/ Nitrite normal

Weekly 10% change; will be doing a 25% this weekend

How much water?  Didn't understand exactly what you are looking for.  It is a 55 gallon tank, I replace about 2 gallons a week from evaporation besides the 10% change.

Anyway, my one Mickey Mouse platy has two chunks out of her tail - like another fish took a bite out of it.  She acts fine, eats like a hog and plays with the other MM platy all the time.  Petsmart checked my water - all is ok except ammonia is a little up but then we just added 10 fish in the past 3 days. I see no sign of ich on any Mollies or anything wrong with any other fish (except the one blue platy that is birthing and is hiding under a bridge and has given birth to 8 fry so far).

Petsmart says I am doing everything right and is at a loss.  Any suggestions?  Can send a pic if necessary.

Thanks in advance!

Answer
Hi Vicki;

It's probably just another fish biting her. As long as it doesn't develop white or reddish areas indicating infection on the damaged part it should heal up just fine. Sometimes fish have little squabbles that we never see. If you begin to see the same injuries on other fish, watch them to see who the culprit is and remove the aggressor if necessary.

I hope all goes well...

At Your Service;
Chris Robbins