CA ALK MAG QUESTION

I can understand your concern.
If I were in your shoes, the first question I would be asking myself is "Why?"
Why do I believe I must raise Mg. Is something wrong with the tank? Are coral or Coralline algae doing poorly?

Your original Alk level, which I would assume was at least 8 dKH and probably around 9 dKH (3.2 meq/l) was good.
Second question I would ask myself:  What was the reason for pushing it up to 11 dKH?

My opinion:
Typically, if coral are opening up with Alk 8-12 dKH, Ca 350-500 and Mg 1200-1400, I would say that all is well. We can cause more problems by trying to mess with the chemistry of our aquarium, than by letting it have it's own balance, with supplements to keep up the minimums, of course. Think of your tank as an individual and Alk, Ca and Mg as food. Not every tank needs the same amount of food and too much food can make an individual unhealthy.

Aloha,
Mark


Edited by Mark Peterson - September 30 2013 at 12:18pm

Just as an FYI, there are salts on the market that would also keep your mag levels where you want them.

Ahh, I see. Yes, Alkalinity at 5 dKH was low enough to cause problems. In my early days, around 1996, I allowed Alk to fall slowly over 8 months to 3 dKH. I was experimenting with doing no water changes and I knew nothing about testing for Alk and Ca (until the end of the experiment ). Those were the days when hobbyists knew very little about Alk and Ca. In my all soft coral tank, pictured below, coral stopped growing. I even traded in my cherished beautiful 4 year old Six-Line Wrasse before I realized he was not the reason for disappearing Hermits.

I'm happy to read that coral are doing better.
Well, 11 dKH is not too high. 16 would be too high.
Just out of curiosity, how many days to raise Alk from 5 to 11?

Aloha,
Mark

75 gal  left side view


Right side