Little confused on your set up. But if you are going to do hypo, there can be no corals, inverts in the tank. Any tank which has had MI introduced to it, will need to go fallow (fishless) for 8-12 weeks. There are different strains of MI and some are stronger than others. As far as hypo, fish only, put in some pvc piping for the fish to hide in. You will need a refractometer, swing arms are too inaccurate. Follorw Leebca's instructions, he is an expert on the subject. Your 90 will be fine after 2 or 3 months of being fishless. Make sure you have test kits on hand to keep a close watch on your water conditions (on hypo tank). It is a long drawn out process, some just say keep your tank stress free and live with it, that may work for some but I would prefer not to have it in my system. Bite the bullet now and quarantine in the future. Good Luck Also remember once in hypo, just because you don't see any spots doesn't mean it is gone, different stages, different degrees of visibility. Good luck