Is dosing mag weekly unusual?

[hopper]

I read in a post earlier that Tropic Marin salt is low on magnesium. I thought maybe this is why I am having to dose mag every week or so. When reading some of the Advanced Aquaria articles I got the impression that mag should only have to be dosed periodically. Am I having to dose more than usual because of the Tropic Marin salt, or is something causing the mag to percipitate out faster than normal. Tests are coming up with around 1180-1200 on the mag every week or so and I add enough to get it back to 1285. Today it tested at 1200 and I added 4 oz. of the epsom salt recipe as the calculator called for. This is in a 110 gal. reef with 10 gal. water changes done weekly. Using Salifert test kits for the tests.

PH - 8.1
Alk - 2.38
Cal - 404
Mag - 1200
Temp - 79
Ammonia - 0
Nitrates - 0
Nitrites - 0

My targets are 2.95 for the alk and 420 for the cal.

[Randy Holmes-Farley]

Have you measured your salt mix?

You should not need a 100 ppm boost to magnesium each week, although the rate that it disappears depend son how much you otherwise add with your calcium supplement system (if any) and what the rate of calcification is, and lastly, what organisms are using most of the calcium and alkalinity (coralline uses a lot of magnesium, while some corals use a lot less).

FWIW, I boost my Instant Ocean by 150 ppm in magnesium with MAG flake before I use it for water changes. That is partly because IO is a bit low, and partly to offset calcification loses.

[hopper]

I don't have any salt water made up as I just did a water change a couple of days ago. As soon as I get another batch made up, I will run a test on the mag and see what it says. I don't really have a lot of corals to speak of as I am still rebuilding from Hurricane Rita last year that just about wiped out the tank. I have a monti cap, frogspawn, candy cane, a small pocillapora (tiny), GSP's, and two clams. So I am thinking that the mag intake shouldn't be that much at all. Also planning on running a test on the tank water next Tuesday and seeing how much has preciped out of the tank in a weeks time. I'll follow up with you next week with both test results and go from there. Thanks for the help.

[Randy Holmes-Farley]

Sounds good. Let us know what you find in your salt mix. :)