If Alk. and Calc. are good, will magnesium be also?

[otrlynn]

I am currently testing for (and dosing 2 part) Alk. and Calcium. If I am keeping the parameters in the recommended range of Alk 7-11 dKH and Calc. 400-420, do I need to be testing for magnesium? I have a 58 gallon mixed reef that is currently light on coral (a few each of softies, LPS and SPS) My biggest user of calcium is probably the Halimeda that I have growing in the display. I do water changes of 4-5 gallons weekly with RO/DI. LFS doesn't carry magnesium test but I will order one if needed.

[seanb1]

your tank will survive without it but

you need to buy the magnesium chloride from bulk reef supply and bring your magnesium up to 1280. you can safely raise it 100 ppm a day.
magnesium is very high in seawater.
yes you will need a mag test kit.

heres a good link on magnesium.

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

[rbursek]

If Mg is low it is hard to get and keep Ca up. What salt are you using?

[BLKTANG]

<a href=showthread.php?s=&postid=12102254#post12102254 target=_blank>Originally posted</a> by rbursek
If Mg is low it is hard to get and keep Ca up. What salt are you using?


Yes if your MG is low its almost impossible to raise,& maintain CA.

I use Saechem Reef Advantage MG.

[rbursek]

Kent Tech M is good and potent.

[kevin2000]

My 02

I think most tanks don't need to supplment MG & suspect some/many of those who have magnesium deficiency have created those deficiencies by dumping too much calc/alk ending up precipitating calc/alk and magnesium.

[otrlynn]

I am using Instant Ocean Salt. RHF, do you have any wisdom to add?

[Randy Holmes-Farley]

It is worth measuring, IMO. My short general discussion on magnesium is here:

The “How To” Guide to Reef Aquarium Chemistry for Beginners, Part 2: What Chemicals Must be Supplemented
http://reefkeeping.com/issues/2007-04/rhf/index.php

from it:

http://reefkeeping.com/issues/2007-04/rhf/index.php#12

Supplementing Magnesium



--------------------------------------------------------------------------------

Magnesium is an important ion in reef aquaria. Like calcium and alkalinity, it can be depleted by various means if appropriate measures are not taken to maintain it. In order to prevent its depletion, or to correct a deficit when it occurs, magnesium supplements are often used.

Magnesium's primary importance in reef aquaria is its interaction with the calcium and alkalinity balance. Seawater and reef aquarium water are always supersaturated with calcium carbonate. That is, the solution's calcium and carbonate levels exceed the amount that the water can hold at equilibrium. How can that be? Magnesium is a big part of the answer. Whenever calcium carbonate begins to precipitate, magnesium binds to the calcium carbonate crystals' growing surface. The magnesium effectively clogs the crystals' surface so that they no longer look like calcium carbonate, making them unable to attract more calcium and carbonate, stopping the precipitation. Without the magnesium, the abiotic (i.e., non-biological) precipitation of calcium carbonate would likely increase enough to prohibit the maintenance of calcium and alkalinity at natural levels.

For this reason, I suggest targeting the natural seawater concentration of magnesium: ~1285 ppm. For practical purposes, 1250-1350 ppm is fine, and levels slightly outside that range (1200-1400 ppm) also are likely acceptable. However, an aquarium's corals and coralline algae can deplete magnesium by incorporating it into their growing calcium carbonate skeletons. Many methods of supplementing calcium and alkalinity may not deliver enough magnesium to maintain it at a normal level. Settled limewater (kalkwasser), in particular, is quite deficient in magnesium, but so are many commercial materials sold for use in calcium carbonate/carbon dioxide (CaCO3/CO2) reactors.

Consequently, magnesium should be measured occasionally, particularly if the aquarium's calcium and alkalinity levels seem difficult to maintain, or if excessive abiotic precipitation of calcium carbonate appears on objects such as heaters and pumps. If the magnesium level is found to be low, aquarists can choose from a variety of commercial and DIY magnesium additives.

All magnesium supplements are fairly dilute with respect to magnesium itself, and it often takes surprisingly large amounts of additives to boost magnesium in reef aquaria. For a large aquarium (100 gallons) requiring a substantial boost in magnesium (200 ppm), the amount of supplement may seem incredible (taking, for example, two liters of typical liquid commercial magnesium supplements).

Suitable magnesium supplements can be commercial additives or DIY versions. How to make and use DIY magnesium supplements has been detailed in previous articles. I would limit the boost in magnesium to 50-100 ppm per day. That limit has nothing to do with the rapidity of the magnesium increase, which can be raised quickly, but with the concern that other impurities that may be present in the additive (ammonia, heavy metals, etc.) might be less of a shock to the tank if added more slowly.

The calculator below can be used to determine dosage requirements:

Reef Chemicals Calculator
http://home.comcast.net/~jdieck1/chem_calc3.html

Substantial additional details on magnesium in reef aquaria are detailed in these articles:

Magnesium in Reef Aquaria
http://www.advancedaquarist.com/issues/oct2003/chem.htm

Magnesium and Strontium in Limewater
http://www.advancedaquarist.com/issues/dec2003/chem.htm

A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH
http://reefkeeping.com/issues/2006-06/rhf/index.php

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

[otrlynn]

Thanks all. I will order a test kit.

[Randy Holmes-Farley]

:thumbsup:

Happy reefing. :)