Yep, every time I do a water change. I do add Magnesium, but I test for it. I no longer add strontium. You will get a lot of different answers on how necessary it is for coral growth. The jury is out. My main purpose for adding Magnesium is not for coral growth but to help maintain the calcium/alkalinity balance. I try to keep it around 1400.

My thought on trace metals is, that except for calcium and magnesium, you are usually adding plenty through frequent water changes. I hate to be a broken record, but the only way to know for sure is to do testing.

Gary