Fungus

I have a Salmontale Catfish and it has what I now know is fungus threads
coming of it's body. They look like scratches from a distance.

I have put anti fungal solution in the tank and it has cleared a lot of the
threads up but he is now finding it hard to swim. He is just under 1 foot
long and he either stays upright for a bit then ends up on his back or swims
for the top of the tank and sinks ack down onto his tail.

Is there anything else I can do for him? I was going to put him into a small
tank by himself but it had a leak

Any help appreiated

Steve