Ich is a parasite and the treatments are well known. Yes I am annoyed that you wrote this mail before doing any research whatsoever about the numerous articles for cures to this very common diesease.
However there are only two proven cures for ich, hyposalinity and copper. Hyposalinity means salinity down to 1.010 for a month or so. Copper means copper. Copper is utterly fatal to inverts, hyposalinity just very risky. So if you apply these cures you need to do it in a separate, bare bottom tank, and you will be keeping the fish in there for 4 to 6 weeks while the disease dies out in your main tank. If you decide to use copper (I use this) get a test kit to make sure you can keep the copper levels correct - too low, ineffective, too high, fatal to fish. Don't think you can treat in the main tank - copper will kill your live rock, and hypo will damage anything other than bacteria.
Changing the temperature down will not help, and will likely make things work by stressing the fish. Fiddling with the lights will not help a bit. Garlic is reputed to work, but is an old wives tale. There are a bunch of reef safe cures around that are very hit and miss in their results - kick ich is notoriously poor. Hyposalinity to 1.014 sometimes help with some strains of ich. Formalin is clinically unproven, but sometimes used on copper sensitive fish. Freshwater dips are proven useless.
Tough luck. Now you know why people harp on about quarantine.