Clamped Fins

Clamped fins happen when a fish seems to "clamp" its fins to its body, sometimes struggling to swim because of it. Clamped fins are a general symptom of stress. Any number of diseases can cause clamped fins. The best way to diagnose the cause of clamped fins is to look for other symptoms. 

If the only symptom that something is wrong is the clamped fins, check for other stressors such as bullying or poor water conditions. Ammonia and Nitrite are going to cause a lot of problems at fairly low concentrations. Even if your water tests good for ammonia and nitrites, you might still need to add some more filtering capacity. It's never a bad thing to have too much filtration.