CYA "Fixed", What Next?

[annifred]

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
TA: 170
FC: 11.5
TC: 12
CH: 425
Na: 3420

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.

 

[mgmoore7]

With a CYA of 100, your Target FC is 7.5 (7.5% of 100) and minimum is at least 5 (5% of 100). If it were me, I would not be flurting with the minimum especially since you are not sure of your CYA reading. Personally, I would probably try to work with a 7-9 range.

As you add acid to bring down the forever increasing PH due to the SWG, your TA will come down too.

 

[txnole]

I'm not comfortable commenting on your plan to lower CYA except to say there is more work to be done there. Specifically to your results, high TA can result in difficult to manage pH and cloudiness. I would plan to address this once you land at a manageable CYA. If you bring you TA back in line, you should get closer to neutral on CSI as a result.

 

[pooldv]

CSI at -0.31 is good. I like it to be -0.3 to 0 to prevent scale. The TFP SWG recomended TA is lower to prevent pH rise which is to prevent scaling. The high TA will push PH up. As you add muriatic acid to lower PH it will also slowly lower TA. Eventually TA and PH will reach equilibrium, probably somewhere between 50 and 80. Keep your CSI between -0.3 and 0 and you will be good. It wi,link extend your plaster life by a decade.

Don't get so fixated on the accuracy of the CYA test. If you think it is between 80 and 90 then use 90 to set your chlorine level. It is only 1 more ppm. More FC is always better than less FC. It is safe to swim up to shock level for your CYA, so having 2 or 3 more ppm of FC is cheap insurance against bacteria and algae.

 

[annifred]

Great, thank you everyone. I will plan on keeping the FC in the 7 - 9 range. I did not know that the SWG caused upward drift on pH - our SWG has only been in for a few weeks and has actually been off most of the time because the FC was way high. I did add a gallon of 8.25% bleach when we drained the pool as insurance and to keep us going while we got the new salt dissolved and other chem adjusted. So it is good to know that I need to keep an eye on pH.

Also good to know that I don't need to be concerned about CSI at -0.3 and I will keep an eye on that too.

All your help is greatly appreciated. I just read the guideline for "keeping your post simple" - so I'll make sure I don't put so many words in future posts

 

[duraleigh]

I didn't read your whole post because I got stopped at your CYA test result. It is far more important than any of your other matters.

I consider any pool with CYA of 100+ as unmanageable. I would urge you to spend 50 bucks or so and replace some water. "soldiering on" is easy to say but not always easy to do.