Help with Magnesium dosing!

GiannisK · Nov 3, 2024

I’m using Brightwell Magnesion P to dose my tank. I had seen this @Randy Holmes-Farley message and understood it to mean that it would be difficult to over-concentrate the magnesium solution. Like Randy suggested, I measured out how much magnesium powder I needed to dose, then dissolved it in 500 mL of RODI water.

I used the formula on the container: Mg = X * V / 64, where X is the ppm I needed to raise magnesium by (it had dropped to the very low 1000 ppm so I needed 300) and V is my tank’s volume in gallons (30). This came out to about 140 grams, and I weighed it out and dissolved it in the 500 mL accordingly. Yes, it did take a significant amount of time on a stir plate to become homogeneous.

I dosed the solution for the past couple of months, and my magnesium slowly but surely increased until it’s at a solid 1280 right now.

But…I just checked my container today and found this giant crystal! So clearly I must have overdone it with the concentration.

Has anyone seen something like this before? Can I re-dissolve the crystals by diluting the solution? There is still some liquid in the container and clearly some was being dosed given my steady increase in magnesium.

Could a new recommended maximum amount of powder to dissolve be recommended?

Thanks!

Randy Holmes-Farley said:
FWIW, 1300 ppm magnesium is just about perfect, being a tad above the ocean average.

It takes a massive amount of magnesium dosing to boost magnesium by a sizable amount.

The concentration of the solution makes no real difference. If you know how much solid you want to dose, dissolve it in some water and add it.

How much do you want to boost magnesium in what size tank?

Randy Holmes-Farley · Nov 3, 2024

Yes, diluting should dissolve it. Use ro/di, not seawater.

Andros Reefer · Nov 3, 2024

What is the best magnesium powder?

GiannisK · Nov 3, 2024

Randy Holmes-Farley said:
Yes, diluting should dissolve it. Use ro/di, not seawater.

Do you have a rough sense of the max concentration for future use?

This Wikipedia page places the saturation point of MgCl2 at about 55 g/100 mL and at about 35 for MgSO4 for 20 C. I dissolved 140g in 500 mL at 23 C so I would expect to not have a problem, and yet I did. Is it the properties of RODI water causing the discrepancy? Or is this table not applicable for what we’re dealing with?

Thanks!
https://en.m.wikipedia.org/wiki/Solubility_table

Randy Holmes-Farley · Nov 3, 2024

GiannisK said:
Do you have a rough sense of the max concentration for future use?

This Wikipedia page places the saturation point of MgCl2 at about 55 g/100 mL and at about 35 for MgSO4 for 20 C. I dissolved 140g in 500 mL at 23 C so I would expect to not have a problem, and yet I did. Is it the properties of RODI water causing the discrepancy? Or is this table not applicable for what we’re dealing with?

Thanks!
https://en.m.wikipedia.org/wiki/Solubility_table

If that’s the dilution, maybe just try warming it. :)

Brightwell products are often anhydrous and so need more water to dissolve.