Phos-Free reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens. It is designed to remove phosphates. But because it combines with the other elements noted it seems that it may also reduce borates, chlorine and possibly other chemicals as well. Does anyone know what chemicals Phos-Free removes besides the Phosphates? If someone is trying to keep borates at 50 ppm, should they avoid Phos-free?

IMHO, the vast majority of pool owners should avoid phosfree and other phosphate removers, not because of what they might remove from the water but because of the money they remove from people's wallets! Only in very few circumstances are phosphate removers really needed.

In practical terms, the amount of other substances that lanthanum will precipitate is negligible. Remember that you add amounts to get rid of, perhaps, 1000 ppb of phosphate which is 1 ppm. Lanthanum carbonate is soluble in water so the "carbon" in the carbonates won't be affected. There is such a thing as lanthanum borate glass, but it looks like this has to be formed via lanthanum oxide and the borate needs to already be in glass form (B₂O₃) and this won't be found in pool water which barely has any tetraborate (B₄O₇^2-). Though I don't know this for sure, I suspect lanthanum will not appreciably react with the boric acid or borate ion in the water.

And I agree with waterbear that phosphate removers should generally not be used except under extreme circumstances of really high phosphate levels (>> 3000 ppb) unless one doesn't mind spending money and trying to vacuum to waste.

Richard

My phosphates are much greater than 3000 ppb and probably higher than 5000 ppb and I have never had an algae outbreak at normal chlorination levels (4 ppm, CYA 80 ppm, SWG). I do have borates in my water but this was true even before I added the borates. I have many customers with very high phosphates also that chloriinate in different ways but as long as the CYA level is taken into account to dtermine the FC level there have been no algae problems. We no longer routinely test for phosphates where I work. We test when there is a recurring algae problem and other water parameters are within line.