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View Full Version : Magnesium staying ideal....normal


110galreef
02/09/2011, 07:42 PM
tank was started about 12 weeks back. 8 weeks back, about 30 SPS frags were added. about 5 weeks back: 2 small clams, about 10LPS frags were added and about 20 more SPS frags & 12 SPS colonies added.

I have been dosing about 40 ml/ day of ALK & CAL & they have been pretty steady. CAL 440 & ALK ~ 9.5dKH. All are params are on spot.

MG was at 1400 4 weeks in and still at 1400 8 weeks in, and was at 1340 last week. have done about 4 WC's of an avg 20gals with IO.

DOes this sound about right......Also I plan to manually dose MG, at what point should I add it....1300 or anything below 1350?

Thanks

HighlandReefer
02/10/2011, 07:45 AM
The amount of magnesium used by coral in comparison to calcium is much lower.

Randy explains this in this article:

Do-It-Yourself Magnesium Supplements
for the Reef Aquarium
http://reefkeeping.com/issues/2006-07/rhf/index.php

From it:

"Magnesium Consumption Relative to Calcium
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Calcium is present in the coral skeletons described in Table 1 at about 35 - 38% by weight, because they are largely calcium carbonate. Consequently, the Mg/Ca ratio ranges from about 0.0025 to 0.12 by weight in corals.

Consequently, for a calcium supplement to be the sole source of magnesium in an aquarium, it would have to include approximately this same Mg/Ca ratio (0.0025 to 0.12) to preclude magnesium's buildup or depletion over time. Obviously, with such a wide range, the exact balance in any given aquarium will be determined in part by the mix of corals and coralline algae being maintained. Fortunately, there is such a large reservoir of magnesium in seawater that it takes large differences between import and export to cause important changes in magnesium levels."
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A few other things to note:

Mag is present in fish foods and this source can increase your mag level some.

The amount of mag used by coral is related to the concentration in the tank water. The higher you keep your mag level, the more mag will be incorporated into their skeletons. The mag level in the ocean has fluctuated over the Milena and reflects the amount of mag in their skeletons due to this. Whether high mag levels are helpful to coral is basically unknown, except that higher mag levels may take more energy for coral to remove it properly when the levels are kept high.

The ocean averages around 1285 ppm mag per Randy's article noted above. Targeting the ocean average seems reasonable since we don't have a lot of information regarding this. ;)

allsps40
02/10/2011, 08:14 AM
I agree. My alk stays at 9-10 and ca 420-450, I have a lot of growing sps in my tank. I only dose kalk for alk and ca. I have yet had the need to dose mag. A good reef salt and weekly water changes keep everything else in check. But that is just me and my reef.

110galreef
02/10/2011, 08:55 AM
Highlandreefer- great explanation! Sounds like unless i dip below 1300 i really have no concern to add any!

allsps40...thanks for the input.

I knew MG was going to be used rather slow in relation to the ALk & CA, just would have figured i would have needed to add a few OZ's or something since I have now gone thru about a Gallon of each CAL & ALK. But then again I have had a decent amount of WC's in a short period of time....for me.

That would be great if one less thing thats needs to be added and spent $$ on.

Anyone know if I made a batch up of MG......kept in a low light area & cap tight how long this should last? 3 mos, 6 mos, yr before I should toss & make more?

HighlandReefer
02/10/2011, 09:22 AM
A mag mix should last for an extremely long period of time as long as you keep the container sealed, for many years at least. ;)

A mag level of 1300 ppm is a fine level to shoot for. :)

If you like, you can add any addtional mag needed in water change water & determine the amount you need to add using the Reef Chemistry Calculator:

Reef chemicals calculator
http://reef.diesyst.com/chemcalc/chemcalc.html