Remove everything from the tank. Replace all the filter material with new material. Clean the tank out thoroughly. Then you can completely restart it for sw
you'll need aragonite based sand, live/dry rock, about a lb per gallon of both. You'll need a powerhead that does anywhere from 10-40x gph
. I'd shoot for 20-30 myself. If you want coral you'll need a new light, if not I'd still get a different light that has more of an actinic color to it. You will want rodi
water or premixed sw
from your lfs
unless you want to buy your own rodi
. And you will need marine salt to mix in the rodi
water if you are not buying premixed.