I agree with more salt, in order to kill ick, the salinity must be at least 3ppt (parts per thousand). Otherwise the new ick hatching out, just laugh it off.
And your FH can take plenty.
By the way it doesn't need to be aquarium salt.
I use water softener salt (NaCl), because you can dump lots in and it dissolves slowly.
It is also only $5 per 50lbs.