Reef Chemistry Question of the Day #48 Epsom Salt

Randy Holmes-Farley · Oct 31, 2014

Reef Chemistry Question of the Day #48

Epsom salt is not optimal for making a large (200 ppm) boost to magnesium concentrations in a reef aquarium because it also contains which of the following:

A. Sodium ion
B. Epsilon ion
C. Chloride ion
D. Sulfate ion

Good luck!

.

Zero Nitrates · Oct 31, 2014

How about D

UNCFAN · Oct 31, 2014

The answer is D

tyler1503 · Oct 31, 2014

The answer is D. I'm getting better at these!

Nice choice for B! I like that.

H2O · Oct 31, 2014

I go with A

Randy Holmes-Farley · Oct 31, 2014

tyler1503 said:
The answer is D. I'm getting better at these!

Nice choice for B! I like that.

Try # 45

https://www.reef2reef.com/forums/re...stion-day-45-brain-teaser-salt-solutions.html

tyler1503 · Oct 31, 2014

Randy Holmes-Farley said:
Try # 45

https://www.reef2reef.com/forums/re...stion-day-45-brain-teaser-salt-solutions.html

Haha nope! I purposely didn't answer that one, it's a bit too tricky for me

Steven@ · Oct 31, 2014

D...
Happy Halloween.

DFW · Oct 31, 2014

D!! That brings up the use of Prime in all my top off, and water change water. Is using Prime all the time ok? I always have added it to all of my ro/di water. I have "reasoned" that since I use Prime in all of my water, I can use magnesium chloride exclusively for mag supplement, thinking that the sulfate would likely come from the Prime. But I never have scientifically confirmed that is in fact the case.

ptreef · Oct 31, 2014

Guess D as well

Randy Holmes-Farley · Oct 31, 2014

DFW said:
D!! That brings up the use of Prime in all my top off, and water change water. Is using Prime all the time ok? I always have added it to all of my ro/di water. I have "reasoned" that since I use Prime in all of my water, I can use magnesium chloride exclusively for mag supplement, thinking that the sulfate would likely come from the Prime. But I never have scientifically confirmed that is in fact the case.

There won't be enough sulfate in degraded Prime to make up that difference. I personally wouldn't use Prime in RO/DI water any way, since I don't see a benefit.

Do you use calcium chloride too? That is the big driver of added chloride relative to sulfate.

For magnesium only supplements, magnesium chloride alone is pretty good. Not perfect, but much better than Epsom salt alone.

DFW · Oct 31, 2014

Randy Holmes-Farley said:
There won't be enough sulfate in degraded Prime to make up that difference. I personally wouldn't use Prime in RO/DI water any way, since I don't see a benefit.

Do you use calcium chloride too? That is the big driver of added chloride relative to sulfate.

For magnesium only supplements, magnesium chloride alone is pretty good. Not perfect, but much better than Epsom salt alone.

Thank you, Randy, for your reply!

I use Prime in case there is some sort of spike of chemicals that make it through the water treatment plant, and/or through my filtration unit. Some in this area have had this happen, and they have lost fish, and coral. And it is supposed to promote a protective slime coat to fish, and I have supposed corals, too.
I have used nothing but lime water since setting up almost 6 years ago, except for the occasional addition of Seachem Advantage Calcium, and baked baking soda. I have dripped it nightly. Your articles were my guide. Thank you for that!

beaslbob · Oct 31, 2014

d (the reason we add magnesium chloride)

Randy Holmes-Farley · Nov 3, 2014

And the answer is... D. Sulfate ion
Almost all of you nailed this one!

Epsom salt is magnesium sulfate heptahydrate, MgSO₄^.7(H₂O).

Since magnesium has a molecular weight of only 24.3 g/mole, and sulfate (SO₄^--) weighs 96.1 g/mole, a 200 ppm boost to magnesium will add 791 ppm of sulfate.

Since there is about 2700 ppm of sulfate in seawater, this addition alone amounts to a 29% increase in sulfate.

While it isn't entirely known what the undesirable effects of elevated or depleted sulfate are in reef aquaria, that shift seems overly large and easily avoided.

The way to avoid it, as beaslbob points out, is to use magnesium chloride for a significant part of the addition. Specifically, since chloride and sulfate provide the vast majority of the negatively charged ions of seawater, using them both in such an addition keeps the relative balance of anions approximately correct. To maintain the seawater ratio of chloride to sulfate after the magnesium addition, one would add about 10 parts by volume magnesium chloride hexahydrate and 1 part by volume magnesium sulfate heptahydrate.

This has more:

http://reefkeeping.com/issues/2006-07/rhf/index.php

Happy Reefing.