What caused this is the biggest point imo, yes u can bump up temp and treat accordingly but if nothing changes it will most certainly come back, I had ick once when I first began fk with a overstocked Overfed tank with very little wc, ever since then I've done wc when my n03 hits 40-60ppm, never have had any ick or any problems since then.
Prevention is the key and wc are ur friend.
Go S. Vettel #1 rb8