We drained our pool (about 50%) to lower our CYA from 180. After draining I measure the CYA at about 100, higher than I was hoping for but we are going to soldier on until it comes down with time through backflushing etc. I find the CYA test quite subjective so consider my result "ball-park" - I tested the 50ppm CYA standard from the TF 100 test kit and came up with 45ppm. The extended test kit directions say that the precision is +/- 15 for levels up to 90, so the error on the standard is about 30%? This seems extraordinarily imprecise, but I guess I need to accept that this is the limitation of the test.
The rest of the chemistry is now:
pH: about 7.6-ish
This seems mostly OK, the pool looks clear. I have two and a half concerns:
Firstly, the TA is higher than recommended for TFP. Before draining the pool the TA was 110. I was surprised when the TA went up after refilling the pool, it started at 150 and is now 170 two days later. I tested the supply water and found it to be 190, I guess that just means we have hard water? From reading pool school, it seems I shouldn't try to drop the TA to reach a target (SWG manual says I should shoot for 100 - 200, TFP says 60 - 80 for a salt pool) unless it is causing a problem. Also, reducing the TA looks like a pain in the whatsit.
Pool math calculates CSI to be -0.31 and warns me that this is potentially a problem number for plaster pools. This number varies wildly with variations in target TA, CH, pH and temperature so I'm planning to ignore the CSI warning for the moment since the TA is within the recommended range for the SWG so I assume I am not going to void the warranty. Can anyone tell me why the TFP recommended TA for a salt pool is so much lower than the range recommended by the SWG manual? The pH test is also really just a confirmation that it is within an accepted range, no need to have a more precise measure?
Secondly. the FC is currently 11.5. The Pool Math calculator says my goal is 5 - 13 for a CYA level of 100, Chem Geek's extended CYA/Cl chart says min 7.3 with target 11.4. If the CYA test is +/- 30 ppm accuracy on the CYA test, my head is spinning about how much to worry about the FC.
My pool is cool (currently 72) and not used often. We occasionally heat it to 80 if we have a gathering, and it is not in direct sun for many hours (shady hillside location). I am planning to shoot for an FC of 5 - 7 and bump it up to 8 or 9 if we anticipate a higher bather load. Does anyone see an issue with this plan?
The final half concern is the CH. Our SWG manual recommends 200 - 400, TFP says 350 - 450 so I'm not too worried about it except it is slightly higher than the upper limit recommended by Circupool so I don't want to void any warranty. Prior to draining the CH was 525, the municipal water tests at 325 so I'm planning to ignore that for now unless you think I might be jeopardizing my warranty for the salt cell.
I hope this long and wordy post hasn't induced narcolepsy and someone has actually managed to read this far. I wasn't sure whether this should be divided into several separate threads for each concern - all the parameters seem somewhat interconnected so I decided to make it one post but if you think I should have divided my questions please let me know. And thanks for your willingness to share your collected wisdom.