Causes of fin rot other than water conditions?

[Tropical]

I noticed a few days ago that my GBR's fins were missing at the ends, on his top, tail, and bottom fins. I assumed it was fin rot, and treated with melafix. I tested the water, and it's fine, 0 ammonia & nitrite, 10 nitrites. I got new fish food just incase that was the cause. Anyone have any idea of what else could cause this?

In a 20 long tank it's just him and 8 neon tetras.

 

[FreshwaterTropical]

It could be fin nipping from your other fish. Trying to eat your fishes fins.

 

[Shane83]

I noticed a few days ago that my GBR's fins were missing at the ends, on his top, tail, and bottom fins. I assumed it was fin rot, and treated with melafix. I tested the water, and it's fine, 0 ammonia & nitrite, 10 nitrites. I got new fish food just incase that was the cause. Anyone have any idea of what else could cause this?

In a 20 long tank it's just him and 8 neon tetras.

Sometimes fin rot can happen with good water conditions, and is usually saprolegnia fungus or a pseudomonas bacteria if its not due to nipping. But in can also sometimes be caused by very hard water or concurrently with a rapidly rising pH after water changes. Do you see any redness around the affected area? This would normally indicate a bacteria.

 

[Tropical]

I didn't notice any redness. I do have hard water though.