Trouble keeping KH and Mg in balance with Ca

[Kmoriarty]

Hey all, my reef has been doing great all in all. I have a few zoas, a leather, a pulsing xenia, one torch, one open brain, and two peices of montipora digitata (the only sps). They are under a 4 bulb T5 with LED moonlights. The corals are all healthy and the leather and leathers are growing readily. The Xenia has taken off and is now a weed. The sps however have not grown much and i think its because i'm having trouble keeping my Mg, KH, and Ca in balance. I have been dosing 2 drops of Brightwell Aquatics "liquid reef" everyday. for the most part it keeps my calcium right around where i want it, as the below results will indicate. However, it always seems like my Mg and KH are a little low. I was contemplating getting a magnesium buffer or dKH buffer, and doing a small amount per day of each. I listed my test results for the last couple months to get an idea of my ranges. Thanks for any advice .

P.S. Tank has been up for about 8 months or so now. Nitrates have been between 0-5ppm for the last few months. I keep my SG at or very close to 1.024. I do weekly 5 gallon water changes. Tank is a 40 gallon. Any other information needed just let me know.

5/20/2011
CA- 475ppm
Mg - 1500ppm
KH - 3.0meq/L - 8.4dKH

5/17/2011
Ca - 465ppm
MG - 1220ppm
KH - 3.1meq/L - 8.7dKH

5/12/2011
Ca - 490ppm
Mg - 1340ppm
KH - 3.25meq/L - 8.85dKH

5/3/2011
Ca -490ppm
Mg - 1320ppm
KH - 3.4meq/L - 9.5dKH

4/26/2011
Ca - 440ppm
Mg - 1380ppm
dKH - 3.5meq/L - 9.8dKH

4/21/2011
Ca - 430ppm
Mg - 1280ppm
dKH - 3.1meq/L - 8.7dKH

4/19/2011
Ca - 490ppm
Mg - 1400ppm
KH - 3.1meq/L - 8.7dKH

4/12/2011
Ca - 475ppm
Mg - 1500ppm
KH - 3.5meq/L - 9.8

[Jason Mraz]

What kind of salt are you using. I think your Ca is a little on the high side and it seems like it goes up and down pretty fast. I have a 125 with monti caps birdsnest, 3 acros and a fuzzy yellow marshall. And some lps and softies. My Ca stays pretty constant, I dose a little bit but I am using Redsea Coral Max pro Salt. They only thing in my tank that drops is the KH and I find myself adding KH buffer once a day or every other day. But I have some pretty heavy duty fans blowing on top of the water because my chiller is a little undersized for this tank so I get a bit of salt creep and about 1-1/2 gal a day evaporation.

[Kmoriarty]

I don't mix my own saltwater. My lfs has good saltwater and ro/di that I use. I tested it once at these three readings were in a good balance. I agree though it is a bit high especially compared to the others. Do you think additional dosing of a mag and dKH buffer would help bring them in balance?

[kevinpo]

Hello,
Your calcium is a bit high and so is you magnesium but they are in no way responsible for the slow growth you are getting from you Montipora coral. At:
Calcium 380 ppm
Magnesium 1320 ppm
Alkalinity 8-9 dKH
You should have from 1/2" - 1" growth per/month with that species. (They grow so fast I don't keep them in my display tank anymore). The growth rate is most likely due to allelopathy or light intensity. Many LPS and SPS corals will not do well in the presence of some species of soft corals such as Leather types i.e. Sarcophyton/Sinularia. For lighting you will need the Montipora digitata to be within 6" or so of the bulbs with t-5's to get fast growth. Moderate to high water flow rates will also help speed up the growth rate. I use 400W halides over driven with a 430W ballast 12" from the coral, so they can take the light if properly acclimated to it.

Cheers,
Kevin