For me a quarantine of a few weeks is not long enough, some cysts can sit dormant for long perIods, I usually consider 3 months a minimum quarantine time, a friend who is in charge of an aquatic exhibit at a zoo considers 6 months minimal.
And since most clowns are either wild caught, or Asian pond raised, the strains for ick from those tropical areas may be very resistant to higher temps.
Here in Panama I have seen ick on fish where water temps were in the 90sF.
Most research on ick, has been done of North American and European strains that are from cooler waters, and not as evolved to resist heat, like tropical varieties can
And because of that reason, I don't bother raising the temps when treating (because those higher temps can make some of the secondary bacterial infections more virulent).
When treating I use salt at least 3 lbs per 100 gallons (resulting in a salinity of 3 ppt), and keep treatment up long after visible spots have disappeared, up to 2 months. I don't using volume (tsps, tbsps, etc, because of grain size,3 lbs of salt is 3 lbs, whether small grain a large, using volume may result in under treatment)
A salinity under that concentration may irritate ick, but not kill them, and to me, salt is much less stressful, and natural to fish, than some of the more toxic medications.