Quoting Ronald Shimek, “Marine Invertebrates”, pg. 128.
“Aquarists often assume that all changes away from natural conditions are negative, but this may not necessarily be the case. Not every material in natural seawater is necessarily beneficial to all organisms, and some are toxic.
Strontium has been shown to reduce calcium transport in coral tissues, and as such reduces the coral calcification rate. Hobbyists sometimes maintain that strontium additions produce denser coral skeletons, without realizing this simply means that coral growth is stunted. Basically the epithelium secretes skeletal material, but the animal’s growth is retarded and thus there is more calcium carbonate deposited per linear distance of skeleton than would occur under normal circumstances. ……………………………………………………………………...
………………………Strontium is probably one additive that could be left out of seawater mixes without any deleterious effects.”
And quoting John Tullock, “Natural Reef Aquariums” pg. 272-3.
“A test kit for strontium is commercially available, but many aquarists…………………...
…………..do not bother to test for this element. ……………………Strontium supplementation is controversial among experienced aquarium hobbyists, with some suggesting that it is unnecessary or even harmful.”
Sometimes doing less is doing more, I think, and easing up on trying to be precise with water chemistry could be doing more. IMHO.
Also, magnesium….of the 4 books that I have read during my reefkeeping infancy, Palletta’s The New Aquarium; Borneman’s Aquarium Corals; Tullock’s Natural Reef Aquariums; and Shimek’s Marine Invertebrates, the former and latter don’t bring up magnesium at all and the other two barely mention it. Heck, I don’t think Baensch even mentions it in his Marine Atlas #1 and that guy is a science junkie! The way I read the lack of magnesium knowledge passed on from these authors is …don’t worry about it! I think if one uses a product such as Seachem’s Reef Advantage Calcium, which maintains magnesium and… yes, strontium too, then your good to go without the added burden of stressing over yet another chemical element.
Adequate and consistent partial water changes will help maintain the chemistry also, from the new salt mixed in.
Maybe test for magnesium once every month or two to satisfy any curiosity.
Anyway, this is all IMHO.
Cheers,