First and foremost, this is a spectacularly educational site! I have learned so much from all the posts. Thank you everyone for generously sharing your time and knowledge.
I need your opinion and advice about a possible RO treatment of the pool (or leaving things as is for the time-being -- for how long? What are the risks?).
The pool is in-ground gunite/plaster with tile waterline plus an overflow spa.
Mostly 10% bleach as chlorine source, muriatic acid for pH control, occasional correction of TA with sodium bicarbonate. No other chemicals to speak of except for boric acid loading about a year ago to introduce the borate.The current water parameters are below (reliable tests, LaMotte colorimeter or lab-quality pH/conductivity/TDS meters):
pH 7.2-7.3 (staying on the lower end because of CH)
Borate ca. 30
There are no serious issues with the pool yet: no algae to speak of; usual brushing takes care of it easily, and the robotic cleaner does its job pretty well too; no visible scaling, although the pool cleaner started to pick up much more grayish "dust" which was not the case before about 2 months ago. The water starts to taste a little "salty" but not a big deal.
Two things I noticed are (1) pretty sudden drop of CYA (was over 140 just 6 months ago, and is now less than half of that. Some minor water changes when filter was back-washed, but not enough to cause such a big drop), and (2) much harder time keeping FC/TC levels up; the other day the overnight drop was from 10 to 3 ppm (acid corrected as usual, then added bleach). Thoughts?
Do not want to drain an refill (and pretty pointless too, the supply water is about 370 CH anyway). Is it time to bite the bullet and do the RO treatment? I do not like the idea of precipitating, flocculating and vacuuming calcium.
All thoughts and experiences are welcome and much appreciated. Thank you!