Magnesium and calcium

[Davesreef’s]

Hey all I have a lps dominant reef as I’ve been addicted to torches recently… I was wondering how accurate is Hanna’s calcium and magnesium testers? I have a magnesium that tested 1110 ppm two days ago and now it reads 1315ppm. I’m not sure to dose or not as I have all for reef dosing currently. Any help?
Thank you in advance!

 

[Reginald Reefer III]

Hey all I have a lps dominant reef as I’ve been addicted to torches recently… I was wondering how accurate is Hanna’s calcium and magnesium testers? I have a magnesium that tested 1110 ppm two days ago and now it reads 1315ppm. I’m not sure to dose or not as I have all for reef dosing currently. Any help?
Thank you in advance!

Not very. Mag is notoriously difficult to accurately test. I have Hanna mag and cal testers, but have used salifert for Mag/Cal and Hanna for Alk/NO3/PO4 when I was getting weird results with Hanna Mag/Cal.

 

[Davesreef’s]

Hey all I have a lps dominant reef as I’ve been addicted to torches recently… I was wondering how accurate is Hanna’s calcium and magnesium testers? I have a magnesium that tested 1110 ppm two days ago and now it reads 1315ppm. I’m not sure to dose or not as I have all for reef dosing currently. Any help?
Thank you in advance!

Not very. Mag is notoriously difficult to accurately test. I have Hanna mag and cal testers, but have used salifert for Mag/Cal and Hanna for Alk/NO3/PO4 when I was getting weird results with Hanna Mag/Cal.

I’ve been thinking of trying Salifert for a little while for these. Didn’t want to buy a calcium checker if there are better options. I love the alk, NO3 and PO4 testers as well. Thank you for the info

 

[rowenaad]

That swing is practically impossible unless you have dosed a ton. I never tried hanna for ca/mg but heard enough reviews saying they are inconsistent. I love salifert for ca and mg

 

[rishma]

There are no home magnesium tests I would personally use or trust. Your data is one of the thousands of examples shared in this forum that indicate test error.

Good news is, you don’t need to test magnesium. If you dose 1-2ppm Mg for every 2.8dkH alkalinity dosed or every 20ppm Ca dosed, you will maintain your magnesium levels.

Here is a good write up.

https://www.reef2reef.com/threads/just-say-no-to-magnesium-testing-rmm-is-born.1017528/

 

[rtparty]

They aren’t accurate or reliable

If you want to test calcium, get Salifert.

Forget testing magnesium completely.

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, I only measure alk and not either calcium or magnesium. I will soon be sending in an ICP to Oceamo to see if my assumptions below are reasonable, but frankly I'd be quite shocked if they were substantially off.

My rationale is specific to my system, but here it is:

I add Tropic Marin All for Reef to maintain alkalinity (in the 7-9 dKH range).

It adds a tiny bit more calcium than needed to balance the alk added. So calcium should not ever fall. The slow rise expected is going to be mitigated by the water changes (1% daily by AWC). I know that works well both mathematically, but also since that's what I did for 20 years on my old tank using an additive with the identical extra calcium (kalkwasser), and calcium stayed in the 400's.

Since a lot of my alk demand is from coralline algae, I expect the AFR is slightly underdosing magnesium. I've calculated the possible effect based on the amount of AFR I'm adding (still pretty low per day) and it is very small. I have added a bit of extra magnesium (a few ppm) to my new salt water, but I expect that is not making any significant difference.