Tank consistently uses more Mg than Ca and Alk

prsnlty · May 23, 2015

Randy, why would a tank consistently use more Mg than Ca and Alk?

Randy Holmes-Farley · May 23, 2015

The only possible scenarios that I can imagine are water changes with a low magnesium mix, or a tank with lots of mangroves and virtually no coral.

Or a testing error.

prsnlty · May 23, 2015

Hmmm don't think it's the wc, no mangroves either... but my mg test kit is only about 5 months old - if that, with exp date of 6/16. However, I have a new backup kit with exp date 5/17. So I gave it a go and you're right but then that would mean my previous kit was incorrect from the day I got it

Randy Holmes-Farley · May 24, 2015

What is it reading and how much has it dropped in what time frame?

prsnlty · May 28, 2015

It drops about 120 ppm in a week. Ca does only about 25-30 ppm and alk stays 9.2-9.5 but average is 9.5

heathd.hd · May 28, 2015

My mag never moved either for almost a year now all of a sudden in the last 2 months it's been eating mag like crazy! Is it just the growth spurt of coralline taking over maybe?

prsnlty · May 28, 2015

My coraline is mostly in my sump. I have some in the dt but not a lot. I am wondering if mg drops more if there is higher po4 than should be. I found my po4 test went bad as well. The tank is good now on that and under .03 (salifert). I really need to get a hanna checker for the po4.

heathd.hd · May 28, 2015

Me also. The other testers are just to hard to be accurate with.

Randy Holmes-Farley · May 28, 2015

prsnlty said:
It drops about 120 ppm in a week. Ca does only about 25-30 ppm and alk stays 9.2-9.5 but average is 9.5

That is, without doubt, testing error. It cannot drop that much. There's no place for it to go. A real magnesium drop might have been 0.3 ppm in that same time.

prsnlty · May 28, 2015

Yes, and that explains why it was consistently off. The test kit was bad from the day I got it. I did replace the kit and retested and it is reading normal. Just goes to show that just because your date isn't expired a test kit can be bad. I have been using Red Sea for testing for a long time and never had this happen until I got that replacement kit. Never thought with a good date on it and a year to go before expiration, that it could be bad. I guess lesson learned. So if anyone else has this issue, retest with a new kit or take it to your LFS (I don't have one) and have them test it for you. I have no idea why it was a bad kit, maybe the shipper didn't care for it properly...