How long can I go without shocking?

[spondell]

The great news is that I don't have a problem (that I know of)! I started the BBB method in June with a good shock to about 22 ppm. It fixed everything. We've stayed in control for the whole summer doing nothing more than adding bleach and acid. My question - is there a point where I should shock anyway? I have no CC and keep the pool between 1 ppm and 6 ppm (check every 2-3 days and add bleach to 6 ppm). I've been going under the assumption that no CC, no algae, clear water and no problems means I don't need to anything more.

Current readings (before bleach and acid charge today)

FC: 1.0
TC: 1.0
CC: 0
pH: 8.2
TA: 110
CH: 340
CYA: 80

Thanks.

15000 gal pool, plaster, cartridge filters

 

[polyvue]

My question - is there a point where I should shock anyway? I have no CC and keep the pool between 1 ppm and 6 ppm (check every 2-3 days and add bleach to 6 ppm). I've been going under the assumption that no CC, no algae, clear water and no problems means I don't need to anything more.

Current readings (before bleach and acid charge today)

FC: 1.0
TC: 1.0
CC: 0
pH: 8.2
TA: 110
CH: 340
CYA: 80

First, I would recommend re-testing your pH 30 minutes or so after an addition of Muriatic Acid... or testing more often than 2 - 3 days. 8.2 is too high and you don't want the pH to be bouncing all over the place. Once your pH is good, then add chlorine to increase FC.

There's no reason to "shock anyway" if the pool water has... a.) no visible algea; b.) < .5 ppm CC; and c.) low chlorine consumption. However, I wonder if your chlorine consumption is low. If you're having to raise FC from 1.0 to 6.0 ppm in just two days, that would be 5 ppm / 2 = 2.5 ppm per day.

To buy some peace of mind I would conduct an overnight FC loss test. If the test result demonstrates a loss of 1 ppm or less, then all is well. See Perform the Overnight FC Loss Test

Hope this helps.

 

[dmanb2b]

yup, what Poly said. If you live in a warm climate and never close your pool, you may never need to shock (OK never may be to strong...we all get lazy sometimes )...otherwise if you do close over the winter, then at pool closing and then maybe opening. That's it

 

[spondell]

Thanks Polyvue and dman. Good suggestion on the overnight test. Here's my before and after.

After adding bleach and acid yesterday:

FC: 6.0 ppm
pH: 7.5

This morning:

FC: 5.5 ppm
pH: 7.6 (as much as you can estimate that color difference!)

For some reason, my pool likes to be at 7.8 - 8.0 pH. I've tried to lower the TA once and it did come down some (130 to 110). I suppose I could do that again to keep the pH in a lower range. The 8.2 I had yesterday was partly because I let it go quite a while without checking and partly because it's been raining all week. Thanks for the feedback on the shock question - it's good to know. Gosh I love this system!

 

[duraleigh]

With your CH in the upper ranges of acceptable, I would keep a pretty close eye on the pH and not let it get in the 8's.

I don't use the CSI but I know from previous posts you will be flirting with the possibility of calcium scale in your pool with that combination.

A little muriatic acid from time to time will reduce both your pH and TA and it's cheap insurance.

 

[chem geek]

The overnight loss rate is normal and given your higher CYA your daytime loss should be not be too high. My guess is that you are seeing a higher than normal chlorine loss due to the high pH since the form of unbound chlorine at high pH (hypochlorite ion) has a half-life of 20 minutes while the unbound chlorine at low pH (hypochlorous acid) has a half-life of 2 hours 10 minutes and the 50/50 combination at a pH of 7.5 has a half-life of 35 minutes. Most of the chlorine is bound to CYA and breaks down more slowly, but I suspect that overall the rate of loss may be pH-dependent.

As Dave mentioned, if you lower your TA over time via acid addition you may find the rate of pH rise to be lower and be able to maintain a pH that isn't higher than 7.7.

 

[spondell]

Thanks all. This is a great help. I'm an engineer by education and am stubborn to boot. Once I know why I should do something, I'm a convert. So, understanding why a lower pH is better, and helps reduce chlorine usage and calcium hardness, I'm on it. I live in Houston and keep the pool going all year. I do plan on having the pool drained, touched up and cleaned this winter, so I get a fresh start on CYA, CH and TA after that. So next year, in addition to having the nice clear water that I have now, I'll get to see a clean bottom to boot!