I have a 54 liter (14 US gallon) community tank with 6 neon tetras and 5 guppies. It's heated at 24 Celsius and is filtered by an UGF (under-gravel filter).
The problem is the neon tetras keep getting ragged/torn fins but I don't think it's fin rot as there is no discoloration at all and after a week or so the fins grow back. I'm pretty sure there are no sharp decorations and all fish are active, healthy (apart from the fins) and eating well. The water parameters are all except-able however I cannot measure ammonia but I don't think this is a problem as the guppies would get red gills if the levels of ammonia were too high. I feed the fish on Tropical Fish flakes and occasionally blood worms. I do a water change once a week (25% ish). They've had split fins on-and-off for the whole time I've had the tank (6 months).
The thing is, although the split/ragged fins on the neon tetras don't seem to be a problem, I don't think it does them any good, so how can I stop them from getting ragged/split fins? Also, could it be a disease of some kind and if so how can I treat it?
Thanks in advance!