Adjusting for SWG - having challenges with TA and CYA

[chumbley]

My SWG (IC40) appears to be done after 4 years (of 12 hrs per day during season). It never quite kept up with demand, so I'm trying to get the replacement to do a better job and longer by making some fundamental changes to the chemistry BEFORE the new one goes in (also decreasing pool run time without sacrificing solar benefits).

Using taylor drop tests to measure. Pool is about 28K. Plaster, SWG, solar, DE. Currently using liquid chlorine (8.25 bleach) to sanitize until water balances and new SWG goes in.

Here are my challenges...

My TA has been 110-120 since I filled the pool 4 years ago. I've been adding MA the last few days and aerating (per pool school article on lowering TA) to try and drive it down to the SWG target of 70. I have tubing stuck in the eyeballs, and return water is creating a nice blanket of little bubbles from both returns, and from the spa spillover. I can easily add MA to lower pH into the low 7's, but TA continues to test at 110. Aeration is allowing pH to rise (slowly), but shouldn't I also be seeing the TA numbers decrease as I dump in acid? I've taken pH down to 7.0-7.2 twice now in the last two days (about 1.5 gallons of MA), and TA still tests at 110.

I had a challenge last year with attaining and sustaining CYA in the 70-ish range. 30-40 seems to be a wall. I kept adding CYA, and it wasn't increasing. The season ended before I sorted it all out. I opened the pool to a CYA of about 20 this year. I've added about 12 lbs to date (which should be about the right amount). I am giving it a few more days to see the effects. Anything else I should be checking? I have not been adding water to the pool, and we have not had enough rain to cause overflow. I have no drains or leaks or automated fillers. I may not have a problem this year - but it feels like I do. It feels like something is consuming CYA...

Other relevant stats:
- water temp: 86
- FC: 7, CC: 0
- CH: 300

Regards,
Jeff

 

[Richard320]

It sounds like you're doing everything right.

Remember, the acid lowers pH and TA. The bubbles only raise pH. So... plug in your numbers into poolmath and see what the next acid dose should be. Then scroll down to Effects of Adding Chemicals and enter that amount of acid. The pH drop will be off some, but the TA reduction is usually dead on. So if it shows you're only going to reduce TA by 6, it might not register on the test even though it happened.

 

[Fiberpool]

Haven't a clue as to why your CYA wasn't increasing. CYA isn't a burn off chemical - once there, it's there. CYA in the range between 30-70-ish is ok, just a Chlorine stabilizer. Your FC is High at 7.0 and CC of 0.0 means your swimming in Chlorine, an equal balance is better. A TA of 110-120 is great for a Plaster/Gunite-concrete pool. Is the water clear, what does it smell like, any algae problems? Most SWG systems need a new generator about every 4-5 years depending on hours used and at what percent. I expect my Hayward t-15 will also, using 22 hrs per day during season. CH is a bit high but I don't think that effects your question. btw, I use 12.5% liquid chlorine to bring up the Chlorine level. Now what is your salt level - ppm?

 

[Jimrahbe]

Jeff,

You say "I've taken pH down to 7.0-7.2 twice now in the last two days".. I find that what works best for me is to take pH down to 7.0 and then check it again in a couple of hours, not the next day... If above 7.3, add acid to take pH down again to 7.0. Just keep doing this over and over (while continually aerating) and you will see TA come down in steps, it will not happen all at once.. For me it takes about two days from start to finish to get my TA from 110 or 120 down to 60. That said, it does not stay at 60 very long before floating back to 80 where it tends to stabilize for a couple of months before I have to do it all again.

Jim R.

 

[chumbley]

Thanks everyone for the quick feedback. I will work to keep the pH in the low 7's until TA gets where I want it. Thanks to Richard for pointing out the "effects of chemicals" section, as that helps me set expectations for the TA shift.

Jeff