Switching from trichlor to SWG

[jagfan]

I was a long time trichlor user until I found this site. Made the switch to bleach a few months ago. When I used the tabs, maintaining the pool was very easy in that I didn't need to tend to it each day after coming home from work. That has all changed since the switch to bleach. I find it time consuming and somewhat laborious. I've read posts about how some lucky folks manage to complete the tasks in 5 minutes each day but I spend anywhere from 15-30 mins a day on these basics. By the time I come home from work, I don't want to test water, mix acid, pour acid, pour bleach, etc. every single day. Living in Florida, our pool is open more than 3 months during the year. I can handle these chores on the weekends but not during the week when I work. I'll stop whining and get to the point now. I've decided to invest in a SWG. Tasks are less burdonsome

Here are my concerns:
1. TA - My TA is 160 (high end for vinyl pool). I've read Waterbear's recommendations. For my vinyl pool, are those recommendations still appropriate?
2. CYA - My CYA is 160 after all the years of tablet use. I don't plan to empty 1/2 my pool water but will try to reduce incrementally over the summer. What impact will the high CYA have on the SWG and overall life expectancy?
3. Borates - I would like to add borates. Rec'd my test strips yesterday.

Waterbear (my neighbor to the south) - hope you and and others can point me in the right directions.

 

[JasonLion]

High TA and a SWG will tend to result in rapidly rising PH. If your PH is stable, then all is well. But if your PH tends to rise rapidly you will want to lower your TA level.

High CYA levels do not cause any problems with the SWG, they cause other problems. High CYA means you will need to run at higher FC levels. FC higher than 10 can cause problems for PH testing. With a SWG you should be able to keep your FC level around 8 and hopefully not have that problem. Another issue with high CYA is that none of the available tests are very precise when measuring high CYA levels. Your actual CYA level might be a fair bit lower or a fair bit higher than what the test reads. Because of that it is good to be conservative and run your FC level a little higher than the recommendation. The largest problem with high CYA levels is if you get algae. It can take a really huge amount of chlorine to recover from algae at very high CYA levels.

 

[jagfan]

Jason, you are right about the test reads. Of course my 2 local pool stores always say the CYA is 100 because that is as high as their test reads. But, my nearby ACE Hardware, uses a different testing system that I've found to be a bit more accurate and more in line with my reads. I don't know what system they use, but the results are contained in small separate vials. About 3 weeks ago the young man indicated my CYA was 140 something. This person appeared to be a novice. Last week, a different guy did the test and he said it was 163. This is the same guy that told the first young man that the household bleach I was using as the sanitizer was "calcium hypochloride" (infohe needed to enter into their computer system). Wow, a 20+ increase in a couple weeks. I don't think so. My good test kit arrived the same day, so I did my own testing and found reading the results a bit difficult. I'm not sure at what point the reading should be calculated - i.e., should the black dot be gray, or should there be no grayness visible at the bottom of the tube? I should mention that I've seen and read the Taylor CYA testing guide and picture.

Back to the SWG. My plan (not set in stone) is to purchase the system from my original pool builder, who will also do the install. They sell the Hayward 40K gallon model. Talked to them a few minutes ago and they highly recommend that I reduce the CYA to at least 100 before they install.

My pool is 3 ft at the shallow end and 6 ft at the deep end. If I empty in 2 foot increments, about how many times will I need to empty? And how long should I wait between re-emptying because I assume the water should be well circulated before restarting the process?

 

[JasonLion]

Depending on what your CYA level really is, you will need to replace 2 feet of water somewhere between once and twice to get CYA down to around 80.

When reading the CYA test, you want the entire bottom of the tube to look a uniform gray white color. The transition between the white background and the black dot should not be visible at all.

 

[chem geek]

See the photos in this link for examples of how it should look.

The lighting conditions make a difference so always do the test consistently. When I asked Taylor what would be best relative to how the test was calibrated, they said to stand outside with your back to the sun so that your body shadows the tube which you should hold in front of you looking straight down. This strong indirect daylight gives a good result. If you have the tube in direct sunlight, you'll see the dot more readily and read about 10-20 ppm lower. Indoors, bright indirect lighting seems to give me results fairly consistent with the outdoor indirect sunlight, perhaps 10 ppm higher at the most.

Richard

 

[Guest]

Ace is using the LaMotte WaterLink Express. Many of their pool dept. folk have no training at all and don't even perform the test properly (nor have they passed Lamotte's certification test for proper use of the system) so beware! IF they entered calcium hypochlorite instead of sodium hypochlorite for bleach then I rest my case!

Your TA of 160 is why your pH is rising and you need to add acid every day and your high CYA also contributes to the reasons that your pool maintenance takes more than 5 minutes a day. If you get your numbers into the suggested ranges it will make a difference.

Adding borates without lowering your TA will not help with the pH stability.

My recommendations would be to:
1. drain and refill to get your CYA down
2. get your TA down to about 70 ppm
After you get the above done you can install the SWG
3. then add the borates
4. (this is probably the most important) test your own water and don't rely on inexperienced and untrained folk to give you water test results from a printout that will overdose your pool.

 

[jagfan]

Thanks Waterbear. I'm in the process of draining as I write. I have 6-8 more inches to go for this first drain, then will start refilling and follow the steps you outlined. How many days should I allow between each drain/refill episode. Of course I will check CYA after each refill.

I have a question about using the magic eraser on my vinyl but will start a separate post for that.

 

[chem geek]

Adding borates without lowering your TA will not help with the pH stability.

Only because I'm picky, I'd like to clarify/expand on this. Adding borates will make the pH not rise as quickly (due to the greater pH buffering), but it will take the same cumulative amount of acid to lower the pH back down to where it was. So you don't save on required acid amounts unless you lower the TA. The following are examples without and with 50 ppm Borates assuming the same rate of carbon dioxide outgassing.

WITHOUT BORATES
pH 7.5 TA 160
over time
pH 7.9 TA 160
add acid
pH 7.5 TA 150

WITH 50 PPM BORATES
pH 7.5 TA 160
over same time as above
pH 7.74 TA 160 NOTE THAT pH RISE IS LESS OVER THE SAME TIME AS ABOVE
over 70% of additional time as above
pH 7.90 TA 160
add 70% more acid than above
pH 7.5 TA 143

So with Borates it takes longer for the pH to rise, but the amount of acid needed to be added "per elapsed time" is the same. The bottom line is that borates alone help reduce the frequency of acid addition, but to reduce the amount of acid over time, which is your cost of acid per time, then you must reduce the TA level (or reduce aeration or target a higher pH) to reduce the outgassing.

Richard

 

[jagfan]

Thanks Chem Geek. Very nice explanation. I've already purchased the borax and plenty of acid but will wait to add the borates until after the SWG is installed. For now my focus is on CYA and TA. I finished the first drain/refill. Still filling but over the skimmer now so I have the pump running and added bleach to the water. I'll keep the pump running and check CYA after the sunset tonite or sometime tomorrow. Then I do the next drain/refill next Thursday evening since I don't have to work on Friday. In the meantime, I'll work on the TA.