ragged fins/tail

Question
-10 gallon set up 8 months ago.  One resident goldfish traveled with us during a move last summer.
-2 or 3 inch goldfish (not fancy), one fan-tailed molly, and a newly introduced algae-eatter and newly introduced tetra (shop owner didnt' know name; it is over an inch, round not narrow, white in color and very fast).
-basic filter system/whisperlite
-water chem unknown

Question:  Why are the tail and fins on our black, fan-tailed molly so ragged now?  It looks pretty sad. Is the new tetra picking at it?  This new fish is extremely fast and the tail/fins on the molly looked fine before, from what I remember. What should I do?  I took out the tetra (and put in a temporary container, hoping it will be okay until the pet shop opens on Mon.) and the molly seems to be less timid and lethargic (could be just my imagination).  Will the fins grow back?  What should I do?
Sincerely,
A mom trying to keep her daughter's tank healthy and peaceful.

Answer
Hi Reb;

I would suspect the new fish or the algae eater. The fins of the victim will grow back, but only if the cause of the damage (aggressive fish) is removed so it can heal. Watch for infection like redness or whitish fungus. Get a remedy at the local fish store to treat it if it does get infected. Make 25% water changes twice a week to keep the water clean so the fish can recover. It really does help a great deal.

Followups welcome

At Yoru Service;
Chris Robbins