Good Morning, Mark. I just saw your pm now as I have a wild few guests in this weekend fom out of town
My TFP attention will be dramatically reduced for a few days as a result
Regardless, Joyful has nailed it.
As far as what to do about it -- Im still forming my opinions about the best balance/management scenario as a sequestrant user over the long term. I spent quite a bit of energy last year trying to work this out and have a few ideas but have not yet implemented them, nor have I needed to.
By way of background, I was able to keep my pool crystal clear and algae-free with TFP despite excessively high phosphates from several years of heavy useage. We're talking at one point as high as 51,000 ppb (whereas pool store say you have too much at 1,000.)
With that said, techs at both Jacks and MM have told me during related conversations that its best to keep calcium above 200 (I'm vinyl) to help carry out spent phosphates, fwiw. Since you're plaster, I'm sure you're already doing this. Neither company has to date issued any guidelines about spent HEDP, and my conversations with both last year suggested an ncl inaction to minimize this aspect. Companies who produce non-HEDP sequestrants (which frankly don't work as reliably) by contrast cite this as a reason to use their products. But EDTA causes a whole other slew of issue and consume a lot of FC to boot.
The only reason Id looked into this phenom rather extensively last year was that I was switching to SWG and manufacturers such as Pentair will not warranty their cells above very small amounts of PO4 because there is emerging evidence that in a certain set of conditions there can be phosphate scaling. (Very high phosphates plus heat plus super high ph inside cell.) Phosphate scale is getting more research attention right now in the HVAC industry and in mfg boiler settings because sequestering is essential.
My swg is a year old and produces exactly the FC I expect it to at this point. Hayward does not have a warranty disclaimer about phosphates - for them to warrant a cell, you take it to a test center.
So in the shorter term, with fresh fill from a liner change, I've not experienced any problem at all.
The problems in attempting to manage spent phosphates is two-fold...the first is that there's nothing in the pool industry the can accurately read the knd of levels I was at.
I solved that problem by purchasing a Hanna hi po4 tester. When I was up around 50,000 ppb I still had to dilute with distilled water.
The second problem is that at super high levels, phosphate remover products will cause a lot of floccing and not always produce the results you'd expect.
I was reluctant to use a remover throughout the year because I was running inside a winter dome and was reluctant to do anything where I'd have to backwash in freezing temps. I may change that strategy next year when the dome goes back up after I tinker a bit.
BUT if one wanted to keep the level of spent phosphates down to avoid the high kind of buildup that over years "might" cause scaling on equipment, this is the rare case where a weekly addition of lanatham chloride, which is Seaclear's phosphate remover, would be a good strategy. When pool stores say this, its baloney about algae. But there can be strategic value in this approach for heavy sequestrant users. Matt (Joyful) is doing an experiment now with this at low levels.)
In my case, my plan as been to do an Alum floc experiment after summer season winds down and I can stand to have the pool out of commission for a day or two before putting up the winter dome. Alum, if it works, will drop both po4 AND metal, and is then vacuumed to waste. Its cheaper and the metal reduction would be an added benefit. But its also very finickity as a treatment and desnt always work right.
To summarize this long and wandering post, here are what I view to be your options, in order of preference
1. Use as much MM as you need to keep the pool looking the way you want it. Don't worry about possible po4 scaling until something goes wrong since I truly believe its rare. But remember that with copper pipes, you ultimately will need do do things to reduce the concentration over time...whch you've already started. One of those things might be a partial water change in another season or two.
Or
2. Get a meter, and if needed, make a plan to manage po4 with weekly or monthly additions of Seaclear (commercial grade) phosphate remover.
Or 3. Consider doing an annual or seasonal treatment via Alum floc, which might reduce your copper ppm as well.
Since at the moment I'm in the #1 camp, I'm not a great source of advice for cost/benefit/perceived value. But after this fall, I might be in a better position to discuss
