YIKES...Mg LOW

[BLockamon]

OK, I just tested Magnesium for the first time in my system. I never bothered before because 1) I mostly use 2-part (although I have been relying on kalk for the last few months) and 2) my calcium was never low enough to clue me in.

Well, I finally got a kit (Salifert), and the reading was ~960 ppm. YIKES!!! My system volume is about 120 gallons, so the chemistry calculator is coming up with ~2200 mL of Kent Tech M.

I know that magnesium chloride doesn't change the pH too much, but I'm still a little concerned about how to add this much magnesium.

Any suggestions on maximum daily dosing?

Thanks.

[BLockamon]

PS, makes me wonder if I should be getting a strontium test kit too!

[magdelan]

I just recently learned that low Mg will effect your LPS extension, the growth of coraline and the make-up stoney corals. My Torch, Frogspawn, and Hammer seem to not be doing well right now. Tomorrow I will pick up a Mg testkit. Everyone seems to swear by Salifert...so I guess I'll go with that even though the rest of my kits are Red Sea.

[Bebo77]

what salt are you using and how often do you do water changes?

[Randy Holmes-Farley]

I know that magnesium chloride doesn't change the pH too much, but I'm still a little concerned about how to add this much magnesium.

Any suggestions on maximum daily dosing?

I'd add 100 ppm per day max (because of concern over impurities) to a high flow area away from organisms. This calculator shows how much to add:

Reef chemicals calculator
http://home.comcast.net/~jdieck1/chem_calc3.html

Before doing that, you might check a new batch of salt to make sure the measurement is reasonably accurate. If a new batch of a quality salt reads less than 1000 ppm, there may be a measurement error.

[BLockamon]

I use Marine Mix Bioassay Formula salt. I recently switch from Kent Marine after getting one of the batches with low (i.e., no) alkallinity. That may have been the source of the log Mg. I never though to check the Mg after switching.

I do water changes about every month (~20%), but its time for a change.

Thanks Randy; I have some salt made up, so I'll test it to confirm.

Assuming that the test is OK, is there anyting else I need to be watching as I raise the Mg. My calcium is ~360 and alk is 9.9 dKH. I need a calcium boost, but I need to get the Mg up first.

[Randy Holmes-Farley]

Nothing special to watch for unless you are using a bag of MAG flake for the first time, in which case you might start slow to make sure there isn't any impurity issue impacting corals. Raise magnesium 100 ppm per day max to allow impurities time to be dealt with by the various aquarium chemistry systems.

[BLockamon]

OK, I tested a batch of my salt water, and it came in at ~1075 ppm Mg. I'm surprised that it's 200 ppm lower than listed, but I guess they aren't 100% homogenous.

My tank is up to ~1050 ppm after 2 days and 16 oz. of Tech M. At least it's headed in the right direction.

[Randy Holmes-Farley]

:thumbsup:

Sounds good! :)