I have used this salt for a number of years with no issues. Recently I noticed that it now has an additive included, by searching the MSDS thes are described as the ingredients:

Sodium Chloride 99.97%
Sodium Hexametaphosphate 0.03%

http://www.cargill.com/salt/products/water/diamond-crystal/dc-pellets-softener-care/index.jsp

The question is in a 10,000 gallon pool how much phosphate in ppm would a 40 lb bag introduce? As it is less than half the cost of pool salt from the local pool store I would like to keep using it but not if it raises the phosphate level too high. This would be especially a concern in a drain and fill situation.

Any help would be appreciated.

Solution would be to use the coarse water softner solar salt sold in the blue bags (100% sodim chloride as is pool salt) vs using softner pellets you have linked above....it may be even a $1 cheaper than the pellets.

Even so 0.03% would be just about 2oz per 40lb bag....not sure how much ppm that translates into, but my guess is it is fairly immaterial.

just picked up 120 lbs (two 60 # bags) from home depot of Sun Gems Diamond Crystal, total $14.00

home depot did not have any blue bags at this location, while they had a generic pool salt, much more expensive than the water softener salt. crystal size is larger, otherwise appear same.

the surface label does not mention anything besides sodium chloride.

Should work fine, but you may want to double check the bags for weight, they are usually 40lb bags, but perhaps they carry different sizes in various regions:scratch:

I have used the Diamond Crystal water softener salt in the blue and in the yellow bag which are 99.7 % salt.
The pool salt is just smaller crystals which dissolves faster and has no additives.

The minor additive in the water softener salt is Sodium Hexametaphosphate.

This product is used in the Boiler industry as a water softener, and anti scaling agent. It is used in detergents, in paint and printing products to keep the pigment evenly distributed and in the photographic industry. In the textile industry it is used to treat hard water to allow the dye to "wash out" properly. It will prevent soap scum from forming on the fabric and interfering with the dyeing process. It makes the color of the yarn even and bright.

Do you remember the old commercial for CALGON? "Ancient Chinese secret". The origianal formulation of Calgon was Sodium Hexametaphosphate.

It is even used as a preservative in some of our food products.

Crest toothpaste uses it in their PRO-Health whitening formula paste.
"Sodium Hexametaphosphate, which delivers cosmetic benefits, is an advanced anti-tartar/whitening agent that works with a combination of effective, but gentle whitening agents that polish away extrinsic surface stains and protect against new stains"

So it softens hard water, helps reduce scaling in hard water, controls Iron and Manganese, helps with corrosion control, prevents soap scum, and reduces tartar in my pool
Seems like it would be beneficial to have this product in my pool water.

From the MSDS the concentration of SHMP in the salt is .03%
So in a 40 pound bag there are 640 ounces. 0.03% is .0003 X 640 = 0.192 ounces per bag.

Don't doze off on me yet. Stay with me. I see your eyes starting to glaze over.

ppm= (1 lb x 120,000)/gallons of water. Say my pool is 30,000 gals
1 pound in my pool would be 4 ppm so 1 ounce(4ppm/16 oz in pound) is 0.25 ppm or 250 Parts per billion.

250 x 0.192 = 48 ppb
So yes, each bag could theoretically increase the phosphate level in my pool by 48 ppb.
A 10,000 gal pool could theoretically have an increase in phosphate level of 144 ppb with each bag.

I have never tested the phosphate level in the water, but surely it must be in the thousands by now with all the softner salt I have used over the years. I don't have issues with algae even under high heat and extreme bathing loads. The water looks clear, has no smell, and feels soft.

Phosphate rich water provides an excellent environment for algae to flourish.
Maybe I should run out and buy some of that expensive phosphate remover.

On second thought, I will simply continue to maintain my free chlorine level at 6-7 ppm with the SWCG and a CYA of 80 and not worry so much about phosphates.

Source: http://www.phosphatesfacts.org/pdfs/Pot ... atment.pdf