Haven't Needed to Dose Mg in 5 months

[reefguyty]

So my system in question is about 400 gallons and I haven't needed to dose any Mg in about 5 months. I have been dosing BRS's 2 part and have done minimal water changes in this time.

My general parameters:
salinity - 1.026
Ca - 430
kH - 7.8

I dose around 100mL Ca and 100mL kH a day.

At the end of May I raised the Mg from 1140 to 1360 over the course of a week.

Here are some of my Mg test results over time (All tests done with Salifert test kit):
6/16 1350
7/01 1375
7/20 1350
8/09 1350
8/27 1400
9/13 1410
9/23 1350
10/1 1410
10/7 1420
10/15 1420
10/25 1380

During that time I haven't added any Mg and did very few water changes. I am not sure how more Mg is getting into this system? My first thought was that I had a faulty test kit.

I use Reef Crystals salt mix and I did some tests on freshly mixed salt water. At 1.023 the Mg < 1300. At 1.026 the Mg was at 1380 which seems consistent about what I read about the amount of Mg in their salt mix.

I am worried that with no uptake of Mg something is off and coral growth is suffering. All the corals seem happy and healthy from the zoas to the acros.

Has anyone else been in this situation?

 

[Joeganja]

I have the same exact thing as you. I dose BRS two part and no magnesium and I do very minimal water changes. Maybe one 20% water change a month. My tanks fine and corals are growing great. I'm gonna guess your system isn't consuming as much magnesium as it is alkalinity and calcium

 

[Randy Holmes-Farley Verified Community Expert]

So my system in question is about 400 gallons and I haven't needed to dose any Mg in about 5 months. I have been dosing BRS's 2 part and have done minimal water changes in this time.

My general parameters:
salinity - 1.026
Ca - 430
kH - 7.8

I dose around 100mL Ca and 100mL kH a day.

At the end of May I raised the Mg from 1140 to 1360 over the course of a week.

Here are some of my Mg test results over time (All tests done with Salifert test kit):
6/16 1350
7/01 1375
7/20 1350
8/09 1350
8/27 1400
9/13 1410
9/23 1350
10/1 1410
10/7 1420
10/15 1420
10/25 1380

During that time I haven't added any Mg and did very few water changes. I am not sure how more Mg is getting into this system? My first thought was that I had a faulty test kit.

I use Reef Crystals salt mix and I did some tests on freshly mixed salt water. At 1.023 the Mg < 1300. At 1.026 the Mg was at 1380 which seems consistent about what I read about the amount of Mg in their salt mix.

I am worried that with no uptake of Mg something is off and coral growth is suffering. All the corals seem happy and healthy from the zoas to the acros.

Has anyone else been in this situation?

Actual magnesium consumption in your case would be about 0.1 - 1 ppm per day (depending on which organisms are taking up the alk and calcium in your tank). Consequently you cannot easily see that depletion with a random variation of perhaps 80 ppm in your testing result.

My recommendation is to dose the magnesium part as directed, and not base the dosing on magnesium readings, because it is designed to add more than just magnesium, and the rise in magnesium will be minimal. In six months (180 days) of dosing 100 mL of the alk and calcium part each day, the recommended magnesium dose would boost magnesium by about 90 ppm.

If you don't want to dose it, I'd at least do some occasional water changes to help keep chloride from rising relative to sulfate (the other main reason for the magnesium portion of the three part).

You are not using tap water, are you?

 

[reefguyty]

Actual magnesium consumption in your case would be about 0.1 - 1 ppm per day (depending on which organisms are taking up the alk and calcium in your tank). Consequently you cannot easily see that depletion with a random variation of perhaps 80 ppm in your testing result.

My recommendation is to dose the magnesium part as directed, and not base the dosing on magnesium readings, because it is designed to add more than just magnesium, and the rise in magnesium will be minimal. In six months (180 days) of dosing 100 mL of the alk and calcium part each day, the recommended magnesium dose would boost magnesium by about 90 ppm.

If you don't want to dose it, I'd at least do some occasional water changes to help keep chloride from rising relative to sulfate (the other main reason for the magnesium portion of the three part).

You are not using tap water, are you?

Thanks for the info! I'll start slowly dosing the Mg. I have been doing about a 30 gal water change a month so maybe that is helping too (about 7.5% of system volume).

I'm using RODI water and I keep a close eye on the TDS meter. The thought of using tap water makes me shudder Especially with Southern California water.

 

[Randy Holmes-Farley Verified Community Expert]

Thanks for the info! I'll start slowly dosing the Mg. I have been doing about a 30 gal water change a month so maybe that is helping too (about 7.5% of system volume).

I'm using RODI water and I keep a close eye on the TDS meter. The thought of using tap water makes me shudder Especially with Southern California water.

Sounds good.

Happy Reefing.