Like I said, I have been using these blocks for close to 6 years and mag and cal remain stable. When I stop using I have to dose mag and cal. I am convinced they work, still have containers of calcium and magnesium powder that I rarely touch. My clam grows well without dosing mag and cal, I just dose alk. Try it and prove it yourself. In my opinion and experience using them there are no negative effects from what I have seen. I also dose trace elements because ICP shows them to be low.
Here is a pic of my 46 bowfront I had for about 4 years, then upgraded to 75 just last year. Even my monti grew well.
I understand how some people are skeptical but the proof is in the pudding. Rarely dose mag have yet to dose cal. Don't get upset with me having a YT in a 46 but he was small, skinny and ripped fins at petco 5 years ago, had words with management and got him for $10 and look at him now.