Chickenparm, You scare me. You say you've been doing this for 4 years and you have a 100g and 120g tanks yet you use tap water to mix up your salt for monthly water changes. How often do you top up? Your evaporation has got to be high. Tap water for that too?
You know you have too many fish and one coral doing OK is not all that great.
Do this, read more, do weekly 10% water changes, top up daily and spend your extra livestock money on a RO/DI system. Get a 30+ gal trash can and keep a supply of water around, heck even a small RO system will be able to keep up with your needs, you may have to space maintance between the two tanks out during the week but no big deal.
Also, learn about your equipment. It IS the life support system of your tanks. Throwing more chemicals in just to make up for bad maintance is not the way to do this. Can that skimmer handle your tank size and load? Are your lights correct for your corals? You won't know unless you know what you have.
Sorry about the rant but sometimes..........