Magnesium addition questions

scyphozoa · #1 04/14/2006, 01:51 PM

Approximately how much Mg does one have to add to their reef on a daily/weekly basis to keep levels at a fixed point? Is the daily uptake of Mg (or precipitation etc.) relatively high in systems with high bioloads?
I am asking this because it seems I have to add a signifcant amount (about 10-30 ppm or more) every three days or so to keep my levels at 1300. Should I doubt my Salifert test results? How soon after addition of Mg should one wait to test? Could I be adding Mg too fast?
(I have only started adding Mg within the last 6 months after discovering my levels were below 1100 at that time.)

steelhealr · #2 04/14/2006, 02:44 PM

What is wrong with your tank that you have to dose magnesium? What symptoms is your tank having that you have to alter the chemistry? SH

DrBDC · #3 04/14/2006, 06:24 PM

I would let it mix up an hour or so before testing the levels to make sure the mag is well distributed. But I just test, and if dosing use the calculator to determine how much to dose, then wait a couple/few weeks. I do regular water changes with my mag and ca supplemented to 1350 and 420 before the change and do 15% weekly. If you are changing with IO it needs a little boost or you may be fighting your supplementation with water changes.

Here is the calculator I am referring to:

http://home.comcast.net/~jdieck1/chem_calc3.html

bertoni · #4 04/14/2006, 07:11 PM

The test will work as soon as the supplement is evenly distributed in the tank, which can vary in time based on flow, etc.

This article discusses organisms that consume magnesium, and might give an idea of why the tank is consuming it:

http://www.advancedaquarist.com/issues/oct2003/chem.htm

PatMayo · #5 04/14/2006, 07:18 PM

Quote:

Originally posted by steelhealr
What is wrong with your tank that you have to dose magnesium? What symptoms is your tank having that you have to alter the chemistry? SH

Most reef tanks need to have supplemental dosing of magnesium. It helps the water to maintain the alkalinity and calcium levels. I use a salifert test kit to determine the magnesium level. Also if your alkalinty/calcium are difficult to get to the proper levels, this can also be a sign of low mag. Test kits are always the best way to check.

Regards.

Pat

steelhealr · #6 04/17/2006, 10:26 PM

Thanks Pat..know that...I have a reef tank. I don't see how anyone can answer that question without asking scyphozoa what his pH, calcium and kH are in the tank and what his pre-level magnesium are...and..again...what symptoms the tank is having. SH

scyphozoa · #7 04/30/2006, 04:35 PM

Just to follow up.....

I had been using an older (but not expired) Salifert Mg test. During this time I was also trying to adjust my Calcium levels. Out of curiosity I tried out the Seachem Mg test. Despite not being as simple to complete as the Salifert, the instructions are better at giving you a pic of what is taking place chemically in each step. You also precipitate out the Ca then measure the Mg. I am not sure but I think Ca was interfering with my Mg results using the Salifert. I seem to get more consistant results with the Seachem thus far although I haven't used it too much yet.

It would be interesting to get Randy's take on the two tests.

scyphozoa · #8 04/30/2006, 04:42 PM

Forgot to add .......Ca was about 420-430 ppm and Alk about 3.4 meg/l at time I first wrote post. (Had to adjust Ca & Alk after H20 change with faulty Kent salt but that is another post........)

scyphozoa · #9 04/30/2006, 05:30 PM

Tested my Mg today using both tests

Salifert says 1290
Seachem says 1250

(Tested Mg w/Seachem on 4/23, results were 1328.
Did 20% H2O change w/ Instant Ocean salt on 4/28 without adjusting Mg.
Have not added Mg at all since before 4/23.
Water changes causing this drop? ..... Will try testing fresh IO water to see what Mg levels are.)

scyphozoa · #10 04/30/2006, 06:14 PM

Fresh IO water made up to SG 1.026 (refractometer) from my bag has Mg level of about 1312 according to my seachem test.

Anyone else tested their IO for Mg?

(As an aside, despite the supposed changes in Mg in my tank all creatures and corals are doing fine and ph is 8.0-8.2 daily. Alk is 3.4 meq/l and Ca is 430)

Randy Holmes-Farley · #11 04/30/2006, 07:38 PM

I don't have an opinion on which if either test is more accurate, but the 1250-1290 ppm levels right now sound just fine to me.

FWIW, I would not try to understand small changes that can be due to many things, including kit variability.