I never have to dose Magnesium, normal?

[Steve1500]

I dose approximately the same amount of soda ash and calcium every day (about 130 ml each). Half of my corals are SPS/acros in a 200 DT. I test Mg with the RS kit and it’s always around 1400. I never dose Mg. Is this normal for the alkalinity and calcium uptake to move fast and Mg uptake to be non existent?

 

[redfishbluefish]

Most likely getting necessary mag in the salt you're using....being added in your water change schedule. I too use very little mag....all comes from my saltwater changes.

 

[vetteguy53081]

If youre doing water changes regularly with a good quality salt, you may never need to dose unless you have coral that is absorbing these elements at a high rate

 

[W1ngz]

Some calcium additives also include magnesium, I know that's the case at least with the Seachem Reef Advantage.

I've actually dropped the magnesium from my last batch of DIY Aquaforest 123 because dosing it was pushing me past my 1500ppm test kit limit.

 

[Randy Holmes-Farley Verified Community Expert]

Real magnesium consumption is about 1/10th of the calcium consumption, or less, depending on the organisms using it. That means the real demand is often less than 1 ppm per day.

Some salt mixes have such high levels of magnesium already, that normal water changes might maintain it. For example, if the salt mix is 100 ppm above your tank water, and you do a 10% change, that boosts magnesium by 10 ppm. That might be as much or more than you used in that time.

That said, it is still desirable to use the magnesium portion of the DIY two parts. I do not recommend that third part based on testing. Base it on the alk and calcium dosed. It will not boost magnesium too much, and helps deal with other issues, such as the accumulation of chloride relative to sulfate.