Hiya's,
All's i can suggest is this
Use a product like Waterlife Medizin P (lots of doses in the 500ml bottle you see)
Dose daily at 50% dosage strength, do a 50% water change daily just before you dose for that day, so day 1 = 50% water out/new dechlo water in/50% meds dose, day 2 = 50% water out/new dechlo water in/50% meds dose (seems a chore but even my friends sticking to it, and when he can't luckily i can do the dosing etc)
Ohh and use dechlorinator also, in bulk as a pond dechlo there's no need not to when it works out like 17p to treat 150 uk gallons
Slowly raise temperature to 30c (if any signs of fish distress lower slowly)
Do this for two whole weeks
May seem a pain, i'm helping a friend out and we were advised to do the above, he's on day 5 of treating and boy the fish seem loads better in just having the 5 days of meds and he's not lost a fish thus far
Daily dosing many say it's not needed, i concur when i had ich the dosage wasn't daily and my ich went away, but from reading some posts it seems as a last resort daily dosing can and in some cases has to be tried
Tony