Hi,

My betta lost the length of his rear fin at some point in the past. I am not sure where it went, but it just disappeared one day. He is a veiltail. Will it grow back and be long again?

Thanks,
mfa

From what i've read they do grow back but it might not be as long. Try and keep his water in pristine condition to help him heal. Also is there any strong currents in the tank? as bettas have been know to chew off their tails if the current is too strong. if not is there anything that might have ripped his finage?

but for the time being keep his tank water clean and use a little bit of aquarium salt to help him heal

If he is young (around 6 mths) old, it should repair itself completely. Otherwise it might never be quite as good.