Brightwell Aquatics Mixing NSW
 

So im trying to dial in my parameters for mixing NSW in my new 20 gallon rubbermaid. I added 15 US Gal of RODI water and 2350g of IO Salt which brought me to 1.026. Ok easy enough, now onto water chemistry.

My first test was for magnesium which came out to 1267ppm. (Im using a Salifert test kit which is still good for the record) Not bad but i was shooting for around 1300. Im using brightwell aquatics products at the moment and reading the back of the powered magnesium supplement..
"Reference: Each g of Magnesion-P will increase the [Mg2+] in 1 US-gallon (3.785 L) of water by 114.4 ppm.]"
Using this reference I figured each gram of powder would boost the mag in my 15 gallons of saltwater by 7.63ppm. To keep things simple I added 5 grams to the new saltwater hoping for a reading of around 1305ppm. After dissolving the powder and retaking the reading, im left with the same amount of mag as before, around 1267ppm.

Am I missing something here? Anyone else using powered brightwell aquatic products and have any similar issues? I remember a few months ago when I tried doing the same thing only with 10 gallons of saltwater, I had to add WAY more than what the instructions stated to get anywhere near what i wanted. Im going to go ahead and test for calcium now.

Try the calculator here. Should help.
http://reef.diesyst.com/chemcalc/chem_calc3.html

Thanks but unfortunately brightwell aquatics isnt on there. Im not sure if any of the other products have similar concentrations.

Calcium came in at 315ppm. Im going to try for around 420ppm so using the instructions once again..

"Each g of Calcion-P will increase the [Ca2+] in 1 US-gallon (3.785 L) of water by 95 ppm.]"

I figure 17g will boost my 15 gallons up to around 422ppm.

Ill dissolve the powder and add it to the NSW and retake the reading in awhile.

Calcium is now sitting at 387ppm, Far less than the 422ppm I calculated it to be. Argh how frustrating!

I added an extra 10g of magnesium, for a total of 15grams in 15 gallons of water and low and behold the numbers matched up this time. I measured an increase of 113ppm per gram per gallon. (brightwell says 114.4ppm per gram per gallon)

To increase calcium I ended up adding another 8 grams for a total of 25g for 15 gallons of saltwater.

I must have screwed up the second test for mag somehow after adding the first 5 grams. Unless the mag reading was off because of low calcium?