Cories have tail/fin damage

[Skater]

I recently moved my bronze cories from a 30 gal to a ten by themselves so I could make sure they were eating good because my fish got most of the food before them. They've been in there for two weeks and have been fine but now I'm starting to see damage on their fin and tail and I dont know what could be causing it. It wasnt there before the move. It doesn't look like anything is wrong really, they act normal, eat, and the fin just looks like its missing a piece, not discolored or anything. They have a ghost shrimp and a snail as tankmates. Any ideas on what the reason for the missing pieces are? Should I just move them to the 30 gallon, they were perfectly fine there. The only thing in the tank is half of a flower pot, which could have damaged the fins, but theres no way it could damage the tail on one of them. Its not too bad, but I'd like to fix it before it gets bad. Sorry for the long post.

 

[msjinkzd]

was the tank cycled? could be ammonia burn. What iis your maintenance routine

 

[Skater]

This is probably too late for you to notice, but yeah it was cycled. All the water was from the 30, I used a filter I had on the 30 as well. I do a 25% water change every like, three or four days, and I have sand, so I just go through and siphon out anything thats on the surface of the sand. They still act fine and I moved them back to the 30 because the heater on the 10 broke. Any help on what caused it would be helpful though. Thanks