I think my betta has velvet?

[marshiemellow]

On the first day I noticed it, he would not eat and his fins were clamped. He also would just lie at the bottom under his bridge, swimming frantically up for air. I shone a torch on him and the tips of his gills were red and the top of his head also had what looked like red dust. (He is a blue fish with a patch of red on his fins) although considering he is relatively new, I am not sure if the red on his head is normal - though it is only visible with a torch.

I put deionised rock salt from the supermarket into his tank (made sure they were dissolved) as advised. And put a few drops of Melafix antibacterial. (I do not have access to other medication at this point in time).

This was five days ago, and since then he's been swimming a little more or not moving at the TOP of the tank. He also eats like normal and seems much better. However, his fins are still clamped and his gills and head are still red (although faded).

How do I tell if his disease is gone? If its still there, can I treat it purely with salt? If so, how much do I do a day/water change?

Thank you

[marshiemellow]

The symptoms above are the only one I have noticed by the way. He hasn't scratched himself against anything and he has no loss of colour. I've also made sure his tank stays warm with a heater.