Dosing Magnesium

[Reefhaven]

I have question about the amount of mag I can dose per day. I don’t want to shock the system. Total volume of water is 240 gallons. Currently, mag is 1170 (salifert test kit) and want to get to around 1325. Using fauna Marin magnesium balling salts and from their calculator it said the dose 2816 ml (2.8 Liters!). I know I can’t do that all at once so want to know what’s the most I can dose per day. I found somewhere that don’t dose more than 1ml per gallon per day…250 ml. Can I dose more??? TIA

 

[Biglew11]

Most will recommend raising it about 100 ppm per day.

 

[Reefhaven]

Most will recommend raising it about 100 ppm per day.

Do you know in terms of ml how much will that be???

 

[arking_mark]

Do you know in terms of ml how much will that be???

1325 - 1170 = 155 ppm

2816ml / 155ppm × 100ppm = 1817ml

 

[Reefhaven]

1325 - 1170 = 155 ppm

2816ml / 155ppm × 100ppm = 1817ml

So a total of 1817ml will raise the mag to desired 1325ppm. Dosing 20 ml per hour for 12 hours be ok? Don’t want to overdose to fast!

 

[arking_mark]

So a total of 1817ml will raise the mag to desired 1325ppm. Dosing 20 ml per hour for 12 hours be ok? Don’t want to overdose to fast!

Nope. You already stated 2.8L for a 155 ppm increase to get you to 1325. Based on that, I just calculated the safe 100ppm increase recommended.

 

[Randy Holmes-Farley Verified Community Expert]

I have question about the amount of mag I can dose per day. I don’t want to shock the system. Total volume of water is 240 gallons. Currently, mag is 1170 (salifert test kit) and want to get to around 1325. Using fauna Marin magnesium balling salts and from their calculator it said the dose 2816 ml (2.8 Liters!). I know I can’t do that all at once so want to know what’s the most I can dose per day. I found somewhere that don’t dose more than 1ml per gallon per day…250 ml. Can I dose more??? TIA

A likely cause for magnesium that low (aside from test error, which it may be) is low salinity. Raising the salinity may be a better option than dosing.

It would take a very long time for magnesium to decline to that level.

I'd try the kit on some of your new salt water before dosing.

 

[Reefhaven]

A likely cause for magnesium that low (aside from test error, which it may be) is low salinity. Raising the salinity may be a better option than dosing.

It would take a very long time for magnesium to decline to that level.

I'd try the kit on some of your new salt water before dosing.

I just checked the salinity and it’s at 1.026/35ppt. My alk was pretty low too at 5.6 but I’m slowing bringing that back up. My cal is 409. Using Hanna checkers for all and cal.

 

[MikeTheNewbie]

What salt mix are you using?
I have the opposite problem with the Neomarine mix giving me 1480ppm

 

[Reefhaven]

What salt mix are you using?
I have the opposite problem with the Neomarine mix giving me 1480ppm

Tropic Marin all for reef

 

[ChaosAquaculture]

Id try to find the root of the mag problem. What are your alk and cal and salinity? - kali

 

[Reefhaven]

Id try to find the root of the mag problem. What are your alk and cal and salinity? - kali

Alk was 5.7, cal was 409 and salinity was 1.026 couple days ago. Going to test it again in a few hours

 

[Randy Holmes-Farley Verified Community Expert]

I just checked the salinity and it’s at 1.026/35ppt. My alk was pretty low too at 5.6 but I’m slowing bringing that back up. My cal is 409. Using Hanna checkers for all and cal.

Perhaps the salinity measurement is not accurate. Magnesium does not just get low on its own. Heavy depletion is about 1/10th of the rate of depletion of calcium, so not usually more than 1 ppm per day with substantial alk and calcium dosing, without any magnesium dosing. It would take quite a while to get to the magnesium level you report this way, assuming no water changes.

 

[Reefhaven]

Perhaps the salinity measurement is not accurate. Magnesium does not just get low on its own. Heavy depletion is about 1/10th of the rate of depletion of calcium, so not usually more than 1 ppm per day with substantial alk and calcium dosing, without any magnesium dosing. It would take quite a while to get to the magnesium level you report this way, assuming no water changes.

I recalibrated the refractometer with BRS solution and it still came out at 1.026/35ppt

 

[Randy Holmes-Farley Verified Community Expert]

I recalibrated the refractometer with BRS solution and it still came out at 1.026/35ppt

OK, so try your kit on some new salt water that you use.

 

[Reefhaven]

OK, so try your kit on some new salt water that you use.

Yeah, I’m guessing the magnesium test kit is bad. I’ll probably bring a sample of the water to my LFS and have them test it. Thanks for your help!

 

[attiland]

Most will recommend raising it about 100 ppm per day.

Mine said no more than 50ppm per day but my experience is no more than 10ppm per day. My Duncan was really upset if I had done more than that.