MG Out of Whack - Despite a lot of Supplement

[QuiGonJay]

Well, I'm a few weeks into trying to solve this and I'm baffled. About 1.5 months ago, my magnesium dropped from around 1250/1300 to 1040ish. Calcium was 370 and Kh9.0 (about normal for my tank which is about 1.5 years old.

Suffering through a bubble algae outbreak and wanted to get the MG back up, so purchased Red Sea MG Supplement (and CA Supplement). Got CA up to 430, though Ph dropped to 7.5. Can't get MG above 1200. I have now, over the course of 1.5 months added nearly 200 ml of MG supplement (in 10 ml increments daily) with no real movement. Today MG tested at 1020ish.

A few other notes:

* Water changes are done every two weeks - about 10% or so.
* I bought a brand new MG test kit. Same results.

Any suggestions - other than the bubble algae and a small patch of zoas (which have always been unhappy), the rest of the tank seems fine (LPS and Softies). Just want to get the MG up and the other parms locked in so I can test usage and get the dosage right. The MG thing is driving me nuts!

Appreciate any advice.

J.

 

[vhuang168]

How big is the tank?

According to the instructions,

1ml will raise 25g by 1ppm


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[QuiGonJay]

45 gallon tank with about 20 lbs of live rock.

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[cougareyes]

How big is your tank, you can safely raise you mg by 100 per day with no problem, my mg supplement would take 4ml/per g to do this. I find keeping ca and dkh much harder to keep it check than mg, which mg test are you using. Also you may find that bubble algae will not be controlled like some other algae, mg and even lighting has no effect. The only think I found is manual removal and I have had good luck with emerald crabs.

 

[thegrun]

It takes a lot of magnesium supplement to raise your magnesium level compared to calcium or alkalinity supplements. The 200mL that you added was enough to raise your levels only a little over 100ppm, but assuming the tank is using some of the magnesium on a regular basis it's not surprising that your levels have not changed given you dosed over a long period of time. You should be dosing 150mL per day not 10mL to see any movement.
On a side note it is very important to follow the testing procedures exactly when testing for magnesium levels, they are very sensitive to variations in the amount of time required to mix the solutions together, deviations to those durations will distort the test results.

 

[QuiGonJay]

Thanks, yes I hate testing mg for that reason, takes a bit longer. Mg. What you say makes sense with what I'm seeing, the instructions said 10 ml per day max to avoid stress, but I will increase th as the a bit.

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[thegrun]

Yes, as posted above 100ppm per day is an acceptable daily Mg swing.