Let's talk about magnesium stress?

[Koan]

(link)

I don't feel like I have a good handle on what magnesium stress looks like in different kinds of plants.

Our standard freshwater GH test for mineral conductivity appears to make the assumption that our plants don't really care if there's some adequate proportion of magnesium in the water or not.

Of course that's not true. But what does that mean for us? How do you handle testing or supplementing magnesium in your water?

 

[Pepere]

How do you handle testing or supplementing magnesium in your water?

I emailed my water district supervisor to find out how many ppm of Calcium and Magnesium was in the water going into the water mains and if there were any seasonal variations.

Our source water is Lake Auburn which is incredibly soft. Nearly all calcium and magnesium in our tap water is added by the water district and they keep it very stable.

I have it written down. Calcium comes out at 5 ppm and Magnesium comes out the tap at 1 ppm.

I boost it to 30ppm Ca, 6 ppm Mg.

 

[Naturescapes_Rocco]

I add 5ppm MgSO4 to my tanks every week, after a 70% water change with RO water.

Mg isn't take up by plants very quickly -- MAYBE 0.2ppm/day+ in high energy setups?

Using my Nutrient Accumulation Calculator, adding 5ppm Mg after a 70% WC gives levels over time like this:



Over time, my tanks (after plant consumption) sit at a weekly min of 5.6ppm and max of 6.5ppm Mg.

I do the same for CaSO4 to add 20ppm Ca to my tank, which results in 25-29ppm Ca min/max over time. So I end up with ~ 4:1 Ca:Mg ratio. I also add 39ppm K through the week, where the initial dose after WC adds 31.5ppm K, and a midweek booster adds ~7.5ppm K.

While we don't fully understand why yet, the ratio of Ca:Mg:K matters. I follow @Burr740's findings that Ca and K should be roughly equal (or K higher), and there should be a approx. 4:1 ratio of Ca:Mg.

 

[Burr740]

That would be perfect in my 17 farm tanks with a variety of both blasting sand and aquasoil, ranging from 0 to 6 kh. As mentioned before Ive played with Mg levels spending months at a time with anywhere from 4 to 20 ppm along with about 35 ppm Ca. Ive not been able to see a clear difference between any of those levels, other than once Mg gets over about 10 ppm it seems to require more K. Which follows the logic of Mulders interactions

I dont believe there is some optimum ratio between Mg and Ca (and K) because so many other factors are in play, including the presence of every other nutrient along with the internal ionic balance plants naturally, and passively strive to maintain. The latter also explains why there needs to be a certain level present in the water irrelevant to what plants actually take in

This is a good general range between the three, in my experience

 

[Sulla]

I add 5ppm MgSO4 to my tanks every week, after a 70% water change with RO water.

Mg isn't take up by plants very quickly -- MAYBE 0.2ppm/day+ in high energy setups?

Using my Nutrient Accumulation Calculator, adding 5ppm Mg after a 70% WC gives levels over time like this:

View attachment 11510

Over time, my tanks (after plant consumption) sit at a weekly min of 5.6ppm and max of 6.5ppm Mg.

I do the same for CaSO4 to add 20ppm Ca to my tank, which results in 25-29ppm Ca min/max over time. So I end up with ~ 4:1 Ca:Mg ratio. I also add 39ppm K through the week, where the initial dose after WC adds 31.5ppm K, and a midweek booster adds ~7.5ppm K.

While we don't fully understand why yet, the ratio of Ca:Mg:K matters. I follow @Burr740's findings that Ca and K should be roughly equal (or K higher), and there should be a approx. 4:1 ratio of Ca:Mg.

How does MG stress manifest observationally? What should we look for is that's the case?