Why is Magnesium dropping so fast?

[Tim Olson]

I've been trying to maintain Magnesium at 1,400 as one of my measures to control green hair algae. Although, the levels dropped about 35 ppm/day between my last 2 water changes (1425 to 1215 in 6 days, using Salifert test kit). What could be causing the drop? Could it have something to do with GHA dying off, with increased levels of GFO?

 

[Tautog]

Water changes will decrease your Magnesium levels due to your salt, which doesn't contain enough Magnesium
Do you have a lot of Coraline algae? This also depletes Magnesium levels

 

[Tim Olson]

Water changes will decrease your Magnesium levels due to your salt, which doesn't contain enough Magnesium
Do you have a lot of Coraline algae? This also depletes Magnesium levels

Thank you ... good point!

I should have clarified, though, that the tests were done in between my water changes. The 1st test was a couple of days after a water change and shortly after I dosed Magnesium up to 1425. The 2nd test was 6 days later, right before I did my water change. So the change was not the result of a water change. Actually my Magnesium levels usually go up after a water change, with the salt I use (called "salinity for reefs" by Aquavitro).

With regard to Coralline algae, I have it on about 1/3 of the rocks, which I transferred over from my old tank. The remaining 2/3rd of the rock is fiji live rock and has virtually no Coralline algae on it yet.

I guess I'll have to do more frequent Mg tests, between changes, to determine a more precise depletion rate.

Thanks again!

 

[Randy Holmes-Farley Verified Community Expert]

35 ppm magnesium drop per day can be nothing other than test error.

Real magnesium consumption is more like 0-2 ppm per day, and cannot be much higher. It really can't be much more than 1/10th of the calcium drop rate.

 

[Tim Olson]

35 ppm magnesium drop per day can be nothing other than test error.

Real magnesium consumption is more like 0-2 ppm per day, and cannot be much higher. It really can't be much more than 1/10th of the calcium drop rate.

Thanks ... I'm hoping it's a testing error, that would make more sense.

Also, to clarify the 1/10th, is that in ppm or percent decrease?

FYI, here's my most recent test data for calcium and magnesium, using Salifert. Does it look like I have testing error?

Date Mg Calcium
7/20 1215 400
7/14 1425
7/13 1390
7/12 1275 410
7/7 1290 412
7/1 1380 425
6/26 1400 425
6/23 1300 430
6/22 1230 380
6/20 1080 315​

 

[GoVols]

Do you have a lot of Coraline algae? This also depletes Magnesium levels

+1

 

[GoVols]

Thanks ... I'm hoping it's a testing error, that would make more sense.

Also, to clarify the 1/10th, is that in ppm or percent decrease?

FYI, here's my most recent test data for calcium and magnesium, using Salifert. Does it look like I have testing error?

Date Mg Calcium
7/20 1215 400
7/14 1425
7/13 1390
7/12 1275 410
7/7 1290 412
7/1 1380 425
6/26 1400 425
6/23 1300 430
6/22 1230 380
6/20 1080 315​

Tim,
If you like mag to be at about 1400 and I do.

The Fritz RPM salt mixes to about:
@ 1.025 sg
Cal: 430 - 440
Alk: 8 - 8.5 dkh
Mag: 1400 - 1420

I'm on the Red Sea "Blue Bucket" but will probably go back to the RPM.

Used regular IO most of my reefing life and it's as good as anything out there but I just don't want to dose it up at this time.

Freddie

 

[Tim Olson]

Freddie,

Good idea ... I'm trying to increase and keep Mg at 1,400, so I'm going to look into Fritz RPM salt mixes. That clearly would be easier than dosing up to 1,400 at every water change.

The "salinity by Aquavitro" I've been using for a couple of years has guaranteed ranges from 1,269 to 1,403 (@ 1.026) and it's still too low. I buy "salinity" from my LFS in 35lb buckets for $50 or $1.42/lb and RPM appears to be the same price per pound, so that's good news.

Thanks!

 

[Randy Holmes-Farley Verified Community Expert]

Thanks ... I'm hoping it's a testing error, that would make more sense.

Also, to clarify the 1/10th, is that in ppm or percent decrease?

ppm.

 

[Tim Olson]

ppm.

Thank you

 

[Randy Holmes-Farley Verified Community Expert]

Thank you

You're welcome.

Which magnesium kit are you using?

 

[Tim Olson]

I'm using a Salifert Mg Profi Test kit. Is this the most accurate kit? I've heard it's the go to hobby kit, but I'd change in a heartbeat, if you think another kit is better.