Dosing Magnesium

dmcoates · Jan 2, 2016

Hey guys

I have some questions about dosing Magnesium.

First of I will explain how I keep my Alk and Calcium in check.

I have a 100 gal mixed reef. Behind the room where my tank is I have a mixing station room with 3 42 gal brute cans. One is for RO/DI water another is for mixed saltwater and the last one is ATO. I auto water change about 1.5 gallon per day with a stenner pump.

I run about 1 tablespoon spoon of kalkwasser per 5 gallons for 9 dKH. That amount of Kalk is not enough to keep my Calcium in check so a add 2 extra tablespoons of CaCl to my mixed saltwater bin. That keeps the tank Calcium ~425 ppm.

Right now I am not dosing Mag but I am thinking I should start. My current level is around 1200. So would it be reasonable to increase my Mag level in my fresh saltwater and dose Mag Via daily auto water change? If so what additives you guy recommend.

Randy Holmes-Farley · Jan 2, 2016

One easy way is to just boost your salt mix by a fixed amount every time, eliminating any need to frequently measure the tank. I did that for many years. I boosted IO by 150 ppm every time with a fixed amount (no measuring).

But over time, IO boosted calcium, and that is no longer necessary (in fact, magnesium got too high continuing this addition past their recipe alteration).

What salt mix and what salinity? Raising salinity might get your magnesium to normal levels.

Here's a DIY magnesium recipe:

Do-It-Yourself Magnesium Supplements for the Reef Aquarium by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2006-07/rhf/index.php

dmcoates · Jan 2, 2016

I am using red sea coral pro salt mix @ 1.025 sg.

Downbeach · Jan 2, 2016

What are you using to measure your SG? @ 35ppt using RSCP your Mg should be near 1400ppm.

dmcoates · Jan 2, 2016

I am using a refractometer to measure and I will calibrate it before use. The display always runs 1.024 and the fresh mixed saltwater is 1.025. I think the difference is just thermal expansion because the saltmix is cooler. And the 1200 mag levels are in my display not the salt mix.

Randy Holmes-Farley · Jan 2, 2016

Boosting the salt mix to 35 ppt (sg = 1.0264) will substantially boost your magnesium so no dosing would likely be needed. Raising tank specific gravity from 1.024 to 1.0264 will boost magnesium from 1200 to 1320 ppm.

But if you want to maintain that salinity, then it is fine to boost the magnesium by itself (which will boost salinity a little, but not a lot).

sonidodecada · Jan 2, 2016

Interesting

dmcoates · Jan 2, 2016

Great good info.
So when mixing new salt with 55°-60° water do you know what 35 ppt (sg = 1.0264) would be once warmed to 79°.
Or would the thermal expansion be a non issue.

Randy Holmes-Farley · Jan 2, 2016

dmcoates said:
Great good info.
So when mixing new salt with 55°-60° water do you know what 35 ppt (sg = 1.0264) would be once warmed to 79°.
Or would the thermal expansion be a non issue.

Depends on what you are doing to measure that salinity. The specific gravity itself (unlike density) does not change much with temperature because the density of pure water that it is being compared to (specific gravity is the density of the sample divided by the density of pure water) is changing similarly, but some devices may give inaccurate readings in the cold water.