Once you start using the RO
water, the diatoms should subside eventually. Snails will not do much as most animals will ignore diatoms for the most part. As long as you are using tap water it will continue to introduce PO4
and silicate into the tank and fuel the algae growth. This is by far more the problem than the lights. I would suggest getting a high quality PO4
granular sponge as most will also help take care of the silicates as well. The coralline will definately recover once the diatoms subside.