Guppies With Split Fins

Hi everyone,

We're still hanging on in there. After a fairly disasterous start back in June we've managed to keep our 9 tetras and 6 guppies in a 54l tank without any further losses....I'm crossing my fingers as I type this (not easy I know!) 

Anyway, we've always had one of the guppies with a damaged tail which was like that when we bought him, it had a chunk missing. It seemed to deteriorate recently but then halted but now two of the others have splits in their tail fins. Can anyone enlighten me as to what might be the cause of this? Is it fin rot? I medicated the tank with myxazin for ten days but stopped over a week ago. The two split fins have only appeared since I stopped the medication. Also I think I may have been overfeeding them recently as the nitrate level only has increased ever so slightly. Could that be what's causing the damage? (I'll attempt to bring the nitrate level back down by stopping overfeeding and water changes, I hope that's right.  )

I'd be very grateful for any advice anyone can give me.
Many thanks.

Thanks FC76, that's good to know. I wasn't sure if they could heal but I can certainly try the water changes and see how they go. I just wasn't sure whether to start another course of medication or not but I'll go for the 'not' for now.

Many thanks. 

Thank you Sue, I didn't know that, so that's very useful. They are straight lines so that means it's damage.

Many thanks and greatly appreciated.