They are are useful and over time some deplete faster than others. Calcium and Alk buffer deplete the fastest.
You should always use a test kit for anything you are adding. If you have no Idea how much is in the water, then how would you know if anything is needed.
The first 3 you listed are usually maintained well just through water changes alone. The test kits for the first 3 are also quite expensive and most hardcore SPS keepers don't test or dose them. They rely on water changes.
Ca, Alk and Mag are the only 3 you need to test and possibly dose.
on the back of all the bottles it said to use weekly as did the LFS. and are very healthy for corals . i still dont have corals but if its useful for the corals than my live rock will like it. i didnt test the water. does any one use the minerals . or can i do without ( ill finish what i have and just do water changes is enough? )
