Adjusting Mg in IO

[abwalker]

I've read Randy's articles about Mg supplementation, but I just want to check and make sure I'm doing it right.

I typically use Instant Ocean salt and mix it with RO/DI in batches of about 20 gallons to a salinity of 34 ppt (1.025). When I test the Mg levels (Elos test) I typically get between 1000 and 1100 ppm.

Using the this calculator I enter 20 gallons total volume, my initial Mg level, and 1250 as a target level and select "Magflake" from the dropdown. The out-put is between 95 and 160 g (depending on the initial value).

160g seems like a lot of magflake in 20 gallons of water (less than 3 water changes per pound of Magflake) Moreover, when I add that much, I get a white-grey powdery coating over the pump, heater, and inside surfaces of the barrel. Is that right? Am I missing something?

What do people usually do to add adjust Mg in Instant Ocean?

 

[alpha0r]

It takes ALOT of mag supplement to raise the levels. The amount seems about right to me. I use IO and I raise the it with the SeaChem product.

 

[naturebatslast]

160 grams is only 1/3 of a pound. The white powdery stuff is probably a precipitate from the epsom salts in the recipe, FWIW, you can also use straight MgCl and 86 the epsom salts. You can drip it or add it to an area of turbulence to avoid it.

 

[reefsmurf]

I'm not sure what the pure composition of magflake is but I can use Randy's 2 part instead as a comparison:

Randy's (3 cups epson salts + 5 magflake) contains 47,000 PPM magnesium.

Here's some shaky math:
Assuming you are at 1000ppm with 1 gallon:

initial: 1000ppm
target: 1250ppm
dosing liquid: 47000 ppm
your volume = 20 gallons (=75708 ml)

47000ppm-1000ppm = 46000 ppm differential. You only want 250ppm increase: 46000/250 = 184. So your volume (20 gallons) needs to be 183 times bigger than your dosing volume to get a boost of 250ppm.

75708/183= 413ml which is about 11% of a gallon.
Reef Calculator says 403ml. Close nuff.


Since it sounds like you're doing only magflake:

Assuming the amount of pure magflake required is very roughly the same to achieve 47000ppm (8 cups of magflake instead of the 8 cups of magflake+epson formula above), you would need 11% of those 8 cups of all magflake.

Dowflake is 200 grams per cup. I'm going to assume magflake is similar:

8 cups = 1600 grams.
11% * 1600 grams = 176 grams.

Close nuff
I have that white precipitate in my 1 gallon jug of premixed Mg.. but as people have said (including Randing in another thread) it's normal.

 

[Randy Holmes-Farley]

The calculator is right, it takes a lot. I add 500 mL of dry MAG flake to my 80 gallons or so of IO.