I'd like to figure out, once and for all, the truth about phosphates. I don't mean the fact that it's a nutrient (along with nitrates and carbonates) for algae. I mean whether 1) it somehow consumes chlorine on its own, not just as part of faster algae growth and 2) at what level of phosphates (if any) does the standard FC/CYA chart not work anymore.
To address these issues, I think one of the easiest things to do is to have TFP users actually measure their pool's phosphate levels. We may very well find many pools with what the industry believes are "high phosphate levels" actually be clear and algae-free at the recommended FC/CYA levels and some such pools start to develop algae at expected lower FC levels and be able to be shocked back to being clear again. We already know some users (waterbear, for example) whose pools have high phosphates (3000 ppb, I believe) yet are algae-free using from the standard FC/CYA ratio recommendations (in waterbear's case, the standard FC/CYA is before he got an SWG and used borates). To this end, there are phosphate test strips from AquaChek (called AquaTrend Phosphate Test, I think) with 50 tests for $10-$18 depending on where you buy it (some descriptions say it's only 10 tests, not 50, but the package says 50). Taylor sells a test kit, the K-1106, that sells for $27.25 and tests for phosphate levels from 0 to 1000 ppb though I suppose that the dilution method could be used to test for higher levels (same with the AquaChek/AquaTrend test strips). Does anyone know if either or both of these are accurate? Pool store tests are free, but I'm not sure I'd trust them.
I suspect that there may be some very, very high phosphate level (10,000 ppb?) where higher FC/CYA ratios than what we recommend may be required, but I could be wrong about that.
I think that one way to convince those that high phosphate pools can still be managed with chlorine alone is to show that many such pools are indeed OK. We already know that pools that get algae are often tested for phosphates, but the converse typically isn't done -- that is, well-managed pools aren't usually tested for phosphates. If they were, then it might show that well-managed pools with sufficient chlorine won't get algae even with "industry" high (what is that anyway -- >1000 ppb?) phosphate levels. At that point, phosphate control would become something more like using an algaecide or copper -- another method of controlling algae, but not the only nor required nor inexpensive way to do it.
Any thoughts about this?