Not sure if I should raise Mg or not...

First, I do ~15% water change every 10 days or so. I do not dose for anything currently. My tank is 125g with a 30g sump, running a phosban reactor (w/ GFO) and an aqua medic skimmer.

Corals are:

LPS-
Duncan
Frogspawn
Acans (2)
Green Tongue

Softies-
Mushroom
Rics
16 different zoanthid/Paly morphs


Parameters:
Temp: 80-82F
Salinity: 35 ppt
pH: 8.1-8.3
Nitrate: 15-20 ppm
Phosphate: 0-0.05 ppm
Calcium: 390 ppm
Magnesium: 1080ppm
Alkalinity: 9 dKH

Last water change was 5 days ago. My Mg levels have slowly fallen 100-150 ppm over the last couple weeks, along with a slight decrease in Ca. My understanding is that if I was to bring my Mg back up, my Ca would also come up some. My question is basically am I low enough to dose or not?

 

You can definitely bring up mag. Calcium won't really raise itself when you add mag though, you need to dose it; it's just less likely to form calcium carbonate when there's a higher mag level.

 

Yes you are.


As a point of comparison
I keep my Mg at 1500. When it drops to 1400, I dose 100ppm. This averages out about every 4-6 weeks.

 

So just dose for Mg for now (and continue keeping tabs on everything else of course)? I don't see anything else concerning there, do I hear agreement?

Sidenote- what's your favorite Mg dosing agent?

 

Get mag up to 1400+, then raise calcium. You can dose mag until you're up that high, a day between each 100 ppm raise. Then cal, until you're at the numbers you want.

 

you hear agreement

I get it in bulk from bulkreefsupply.com

As it is just an element on the periodic table, I see no reason to buy the expensive bottles of solution, etc.

Agreed and would bet once your Mg is over 1400 your Cal will magically be over 400 (or very close).

 

you might find this thread mildly interesting

http://www.3reef.com/forums/water-chemistry/peredhils-past-year-so-parameters-89142.html#post901024

 

K+ for the help, thanks.

 

So I brought the Mg up to 1160-1180, Ca is already up to 400. I dosed to bring the Mg up another hundred or so this morning, I'll test again this evening.

 

good to hear.. I appreciate hearing positive feedback when some good advice worked out.