Chemistry question

[untamed]

...in a 50 gallon system with only a couple of clownfish, you may not be experiencing much Ca/Alk declines. In fact, start measuring both of those regularly before you start dosing anything. If they are stable, don't go messing with additives.

Regular partial water changes might keep you running along just fine. I wouldn't complicate things until you have to.

Now...tell us that you're Ca is falling from 400ppm to 350ppm over the course of 3 days...and you need to learn about Kalk and additives, quick.