It would be a good idea to test you parameters first. If ph and alkalinity are within range, check calcium. I keep mine around 420 with Turbo-Calcium by Kent Marine, it doesn't seem to affect ph. If needed, I dose with small amounts of potassium iodide and magnesium, but that's it. My 55 is full of zoos, and they grow like crazy. I have several softies, all doing great. Good luck.
I would always test before dosing any supplement. Some good test are Calcium, DHK / alkalinity, and Magnesium. These are related to each other and will affect your dkh level calcium and ph level. after that is stable and you have a "bio-load" of soft corals test Iodine levels.
I would not add Iodine unless the level was low but usually it takes a pretty good bio load to deplete the iodine that is mixed into the standard salt mix like reef crystals. with just zoas and shrooms you should be good with out supplementing between water changes.
For coraline calcium is essential. A lot of people use all these expensive supplements but i use just regular pickling lime from the grocery store mixed in with my top of water. I use a 5 gal jugg of ro/di water and put about 5 tablespoons of pickling lime in it and shake it up real good. If you use this method make sure you shake the jug everyday before adding because the stuff will settle to the bottom. My purple coraline took off through the roof when I started with pickling lime.