Ya. I like to use shortform. oops
400mg/l is definitely enough for ur corals. Actually, anything with 300 - 400mg/l is fine. Mushroom and button are soft coral. They dun calcify as much as LPS or SPS. Note that LPS/SPS are stoney corals.
Magnesium will drop overtime. But its not so drastic as dKH or Calcium. I did not bother abt magnesium until I start SPS. A gd article from advancedAquarist on Magnesium and what adsopt it. http://www.advancedaquarist.com/issues/oct2003/chem.htm
" Magnesium has tremendous biological and chemical relevance to reef aquaria. Fortunately for reefkeepers, it is present in abundance in seawater. There is, in fact, a fairly high turnover of magnesium in reef aquaria with rapidly calcifying organisms. The primary reason that magnesium is not more of a daily concern to aquarists is that the reservoir of magnesium in seawater is very large. Magnesium might be compared to a large lake, with the lake level only slowly responding to changes in inputs from rivers and export via evaporation and the outlet. Consequently, maintenance of magnesium levels is not typically a rapidly developing problem. If using an appropriate salt mix, it may never become a problem for many aquarists. Nevertheless, over the long run the levels can change significantly if the inputs and exports do not roughly match."
Cheers
JC
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