I was getting a lot of algae in my pool. Leslie's measured the phosphate
level at 2500 ppb (actually it was over 2500 but the test kit tops out
at 2500). A good level is about 100.

Leslie's sells PhosFree. A 3 liter bottle costs about $38, and it would
have taken at least 8 bottles ($304) to reduce the phosphates to an
acceptable level. Even the guy at Leslie's said to forget it, just drain
the pool and refill it.

I went to another store (Pool Guys), and they sell Orenda Technologies
PR-10000. 1 quart is supposed to reduce phosphates from 10,000 to 0 for
a 10,000 gallon pool. So for my 40,000 gallon pool it would take 1 liter
to go from 2500 to 0. A quart cost $60 at the pool store (though now I
see it on-line for less). The pool store guys had never used it, as it
was a new product they carried. With much trepidation I shelled out $60
for a motor oil bottle size of this liquid.

I applied it in four doses over two days, mixing 8 ounces with 120
ounces of distilled water, and pouring it around the pool and scattering
it over the water. It precipitates with the phosphates and forms a
flocculates that are filtered out, so your water turns a milky color
until you filter out the particulates. I used the regular filter, as
well as my Dolphin pool cleaner which collects debris in its own cloth
filter bag.

After all four doses I went to clean the four PentAir cartridge filters
which were now sot down the precipitate and weighed at least 2x normal.
Today I had the phosphate tested again and it was down to 200! Amazing.

Even for maintenance, it's much cheaper to buy the PR-10000 which if I
calculate correctly is 15x as concentrated as PhosFree, and just use a
couple of ounces, than to buy the PhosFree. Which is probably why
Leslie's doesn't sell the PR-10000 or any of the other concentrated
phosphate removers on the market.

I checked the data sheet for what's in PR-10000 but they just say that
it's proprietary.