Actually it depends on how bad. But it takes a loooong time.
ime My friend and I went to give away a Midas with a single 1cm deep, and 1cm wide hole to the lfs. I came back almost a year later and it was still at the lfs but the hole healed up and there's a hole but not half as bad.
And me I bought a $500 FH at that same store that had HITH and I healed him up. In a year all holes disappeared. Always near broke and bought a $500 fh with hith. How can I forget how addicted I was, so it's a true experience. They do get better.
HITH med & Lots of water changes & time is all it takes. Have fun with the rescue
