Reef Chemistry Question of the Day #79 Magnesium Supplements

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #79

You determine that your reef aquarium is low in magnesium, and you begin to wonder what the most potent solid magnesium supplements might be.

There are many to pick from, and it seems a perplexing question...

If you add 1 gram of each of the following to a 100 gallon reef aquarium, which of the following will cause the largest boost to the magnesium ion concentration, and which will cause the smallest boost?

A. Magnesium hydroxide
B. Magnesium oxide
C. Magnesium chloride
D. Magnesium chloride hexahydrate
E. Magnesium sulfate
F. Magnesium sulfate heptahydrate

For purposes of this question, ignore anything else the non-magnesium part of the additive might do. So you are not picking the best additive, just the most and least potent ones.

Good luck!





























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[Cory]

If anyone was thinking what is "heptahydrate" like me, here:

Heptahydrate:
1.
a hydrate that contains seven molecules of water, as magnesium sulfate, MgSO 4 ⋅7H 2 O.

I'm going to guess magnesium sulphate heptahydrate gives the smallest boost and magnesium chloride gives the largest boost. So F and C. But only because I'm thinking because heptahydrate is having more water molecules it's heavier with less magnesium per gram.

 

[beaslbob]

d
(6 waters)

 

[beaslbob]

Woopsie
F
7 waters. LOL

 

[Randy Holmes-Farley]

Woopsie
F
7 waters. LOL

And which is most potent?

 

[Rjramos]

I need to know this answer cause right now I've been adding a liquid this C and E and after 80ml in a 120 gal it has not moved from 1230! So, following along.

 

[Rjramos]

I need to know this answer cause right now I've been adding a liquid this C and E and after 80ml in a 120 gal it has not moved from 1230! So, following along.

80ml/Day for 4 days now and 1230 still.

 

[Randy Holmes-Farley]

I need to know this answer cause right now I've been adding a liquid this C and E and after 80ml in a 120 gal it has not moved from 1230! So, following along.

Magnesium supplements require large amounts. This calculator may help:

Reef Chemistry Calculator

 

[beaslbob]

And which is most potent?

I guess I'm gonna find out. LOL

 

[beaslbob]

Magnesium supplements require large amounts. This calculator may help:

Reef Chemistry Calculator

+1
My first magnesium dosing was with just Epsom salts to get a 3 year old tank on old instant ocean, no water changes up from ~700 ppm. It took like 4 pounds or so of the stuff.
Another much more advanced reefer had to do the same thing with his much more advanced tank.

 

[beaslbob]

And which is most potent?

dern
read the stupid question
or is that red the question stupid. LOL
magnesium chloride.
plus I screwed it up anyway in reverse. other stuff doesn't dissolve mag oxide and mag hyrdox don't dissolve very well
I think
lol

 

[Rjramos]

So what is the best magnesium boosting supplement? Magnesium chloride? I need to get my magnesium up and the mag sulfate/ mag chloride diluted in RO/DI water I'm using is not putting a dent on it! Lol.

 

[tyler1503]

E or F will be the smallest and A will be the biggest

 

[Randy Holmes-Farley]

So what is the best magnesium boosting supplement? Magnesium chloride? I need to get my magnesium up and the mag sulfate/ mag chloride diluted in RO/DI water I'm using is not putting a dent on it! Lol.

Add more.

 

[Cory]

You want a magnesium supplement that's ionically balanced so magnesium and chloride rise in proportion. Usually magnesium sulphate and magnesium chloride. But I don't know the amounts of each. You will need to add tons, like cups and cups for 100ppm (based on tank size). It surprised me too when I added it.

Don't forget your salinity will rise too.

 

[Rjramos]

Thanks Cory! Well I just started checking my mag. With frequent NSW changes I never thought it would become so depleted over time. Alright so TONS to get it back up to at least 1300! Lol. What's the maintenance dose like? Can it be maintained with manual additions? How frequent?

 

[NobleSun27]

I have my doser set to add mag once a day at 7ml on a 75g mixed reef and my mag has never gone below 1350 and that's with 10 gallon weekly water changes. Anyway. I think A is the strongest and B is the lowest but I'm guessing bc this is something I have not yet had to think about. I have went the route of calcium carbonate and potassium bicarbonate for my aquaponics tank but never used on my salt tank mmm...

 

[Cory]

Thanks Cory! Well I just started checking my mag. With frequent NSW changes I never thought it would become so depleted over time. Alright so TONS to get it back up to at least 1300! Lol. What's the maintenance dose like? Can it be maintained with manual additions? How frequent?

A lot of salt mixes cheap you on magnesium. I guess to save money. I had 1200ppm magnesium and had to add 36.1 tsp to my 38 gallons of water to get to 1300ppm. I wouldn't worry about a maintence dose as it doesn't get depleted too fast. Unless you have a lot of corraline algae growing- they love magnesium. Instead I'd check your levels monthly or biweekly and adjust accordingly.

The reef chemicals calculator is very good. Use that. For balanced magnesium, instead of using Epsom salts only (magnesium sulphate), I use seachems reef advantage magnesium. IIRC its balanced not to increase the sulphate and chloride, but keep them in balance. That's why magnesium sulphate (Epsom salt) shouldn't be used, because your sulphate will get unnaturally high compared to chloride.

That said, water changes suck at replacing magnesium because they cheap on it. Instant ocean is one.

 

[Randy Holmes-Farley]

Rjramos, what is your magnesium level?

One issue with NSW water changes to supply magnesium is that if you do not maintain at least 35 ppt (sg = 1.0264), you will never attain natural levels of magnesium (1280 ppm).

 

[Randy Holmes-Farley]

And the answer is...

B. Magnesium oxide is the most potent

F. Magnesium sulfate heptahydrate is the least potent

Here are the percentages of magnesium in each:

A. Magnesium hydroxide 41.7% magnesium
B. Magnesium oxide 60.3% magnesium
C. Magnesium chloride 25.2%
D. Magnesium chloride hexahydrate 12.0%
E. Magnesium sulfate 20.1%
F. Magnesium sulfate heptahydrate 9.9%

That said, potency should not be the deciding factor in selecting a magnesium supplement.

A and B, while most potent, will boost alkalinity, and for any reasonable magnesium boost, alkalinity will likely rise too much. They are poorly soluble in fresh water, but will slowly dissolve in an aquarium.

The best supplements will be a mixture containing mostly chloride and some sulfate (about 10:1 by solid volume or weight). Whether you pick anhydrous or hydrated versions doesn't matter, except to know how much you need.

These have more on magnesium and supplements:

Do-It-Yourself Magnesium Supplements for the Reef Aquarium by Randy Holmes-Farley - Reefkeeping.com

Aquarium Chemistry: Magnesium In Reef Aquaria ? Advanced Aquarist | Aquarist Magazine and Blog

Aquarium Chemistry: Magnesium And Strontium In Limewater ? Advanced Aquarist | Aquarist Magazine and Blog

A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com