High CYA, High Alkalinity/Hardness

BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
I'm in my second summer as a pool owner after purchasing a house last summer. I towed the same line as the previous owner and used Clorox Xtra Blue tabs and used basic testing strips. I didn't notice significant issues last year, but also wasn't looking as closely.

This year startup went well (as far as I know from a test strip) and the pool as been ok. I started noticing that I was getting a consistent yellow-ish algae coming around if we didn't brush the pool for 2-3 days. I went digging and found this blog and some really great information. I purchased the TF-100 kit and started using it last week.

The CYA level was beyond the 100 mark. I stopped using the chlorine tabs and began using liquid chlorine to keep my levels consistent. However, the CYA level hasn't dropped in a week. Meanwhile, my pH has remained low at around 6.8-6.9. To make matters worse, after a week long trip to Alaska we returned to find our friends didn't keep chlorine levels up. The previous owner had some calcium hypochlorite pool shock, so I used that to get levels back to normal. In the process, the alkalinity and hardness shot up and have remained high. I would use a pH increaser to offset my CYA problem, but the high hardness and alkalinity stand in my way. I reconnected a homemade 'fountain' to spray some water and increase pH, which moved it from 6.8 to 6.9 over the last 24 hours.

I guess at this stage my question is whether the CYA level will decrease if I continue to add liquid chlorine. Or, whether I need to drain the pool partially and start over with proper management of the CYA and pH. Hot mess, but I'm confident I'll get it under control know that I'm finding good sources of education. Thanks in advance for the insight.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
28,438
Northern NJ
Welcome to TFP.

You need to do the CYA dilution test to see how much over 100 your CYA is...

For CYA > 90ppm, repeat the test adjusting the procedure as follows:
  1. Fill the mixing bottle to the lower mark with pool water.
  2. Continue filling the mixing bottle to the upper mark with tap water.
  3. Shake briefly to mix.
  4. Pour off half of the contents of the mixing bottle, so it is again filled to the lower mark.
  5. Continue the test normally from adding R-0013, but multiply the final result by two.
You will need to drain 70% or more of your pool to reduce your CYA to 30-40. Your CYA will not come down with using liquid chlorine.

Using the Clorox Xtra Blue tabs added copper to your pool water which is another reason to do a significant drain of your pool.



Please create your signature with details of your pool and equipment.

Post a complete set of your water chemistry...

FC
CC
pH
CH
CYA
 

BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
This was what I suspected after perusing the site. Really appreciate the response and high CYA test trick. Here's the chemistry:

FC - 3
CC - 0.5
pH - 6.65 (I brought a sample to work to use our calibrated high-end pH meter since one with the TF-100 didn't come with proper calibrating solution)
CH - 400-450
TA - 70
CYA - ~195
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
28,438
Northern NJ
You can keep on doing dilution tests but at CYA of 195+ you are looking to need close to a complete water replacement.

Take your water to a Pool Store and have them test the water for metals. Lets see how bad your copper is. That will determine is a Water Exchange could work on your pool or if you need a real drain to get rid of the copper.

Read Draining - Further Reading

How are you measuring your pH?
 

BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
I bought a cheap $20 pH meter from TF tests with the TF-100, but it was reading 6.9 since I believe they sent it with the wrong calibration solution. We have a $150 meter at work that gets calibrated weekly, and it read 6.65.

A local pool supply told me there was 'some copper' in the water when he looked at a sample today, but also suggested draining due to the high CYA. He couldn't seem to believe 195ppm could come from one year of using trichlor tabs. As noted, I moved here last summer and perhaps the previous owner was also adding stabilizer. I only ever looked at CYA from the test strip method and it has always read in the middle range of those strips. He suggested I use pH increaser immediately to bring it up over 7.2 pH, even if I'm ultimately going to drain it soon.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
28,438
Northern NJ
I agree you should raise your pH.

pH increaser is sodium carbonate or soda ash.

The best way to raise pH is by aeration of the water. That will raise your pH gradually while not affecting your TA.

If TA is 50 or above, bring your pH up to 7.4 or so using 20 mule team Borax.....soda ash is not a good choice as it will raise the pH and raise the TA a lot.

If TA is below 50, then bring the TA up to 50-60 using baking soda and THEN raise your pH to around 7.4 using 20 Mule Team Borax.

 

BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
I have rigged up a DIY PVC 'aerator' on one of the return ports, but it hasn't done much for the pH over the last 3 days. I have a TA of around 60-70, so I'll look into the Borax. Thanks!
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
28,438
Northern NJ
Any idea on the dosage rate for the Borax (e.g. how many #s to move pH on 20,000 gal by X?)

Use PoolMath Effects of Adding feature.

For a 20,000 gallon pool each 1 lb of Borax raises pH by 0.1 and TA by 1.6.

Since you need to raise your pH by 0.6 I would add 4 lbs, let circulate for a few hours and retest. Then add more as necessary.

Pool volumes are not always accurate and neither is dosage. Better to add in a few doses and sneak up to the desired result.
 
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BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
I just found the PoolMath link and was coming back to report! I was getting more like 10# but I like the incremental approach. Really appreciated the help.
 

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BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
Added 4# of Borax last night, waited about 2 hours and pH was looking marginally increased. I added 4# more this morning and waited 2 hours. My work pH meter shows a rise from 6.65 to 6.88. The CYA must have a buffering effect. It's kind of a scholarly exercise at this point, as I'll drain and refill over the weekend. But, I might add 4# more midday to see if it starts to break free from that buffer. I was also rolling with a TA around 70, so I should still be ok on that front given the calculator estimate above would land me around 80 now.
 

BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
Added 4# of Borax last night, waited about 2 hours and pH was looking marginally increased. I added 4# more this morning and waited 2 hours. My work pH meter shows a rise from 6.65 to 6.88. The CYA must have a buffering effect. It's kind of a scholarly exercise at this point, as I'll drain and refill over the weekend. But, I might add 4# more midday to see if it starts to break free from that buffer. I was also rolling with a TA around 70, so I should still be ok on that front given the calculator estimate above would land me around 80 now.
I should also note that I was using the PoolMath calculator on the website, not the app. When you factor in the new Alkalinity of 80 and new Borate of 5, it shows a need for 6.7# more Borax to go from 6.88 to 7.2 pH. Not sure why the App is different.
 

BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
CYA does not buffer pH.
4 lbs of Borax in your pool volume will raise your pH 0.3.
Not sure why I get the divergent result of having 8# raise the pH by 0.23. Here's the original calculator from the website which suggested 12# based on my actual chemistry
 

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BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
Be sure to read the disclaimer on pH adjustments as shown in Poolmath.
Mights as well put YMMV in the disclaimer ;) Indeed, 6.65 is quite outside the 7.2-7.8 range and TA was below when I started. We adjust pH in brewing water everyday in my day job and it can be pretty non-linear (ex. it takes alot of phosphoric acid to get a pH from 7 down to 5.6, and then hardly any to go from 5.6 to 5.0).
 

BowserB

Silver Supporter
Jul 29, 2018
632
"Old" Katy, TX
Don't you want to do your water exchange first? All the other stuff will be down the drain, so to speak, when you change out your water.
Or did I miss something?
Since you're going to put new water in, have you tested your water supply for pH, calcium hardness, and TA? BTW, since you have access to a super accurate pH meter, why don't you get some tap water (presumably not acid like your pool) and test it at work, then use water from the same sample to calibrate your TFP meter?
 

BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
Don't you want to do your water exchange first? All the other stuff will be down the drain, so to speak, when you change out your water.
Or did I miss something?
Since you're going to put new water in, have you tested your water supply for pH, calcium hardness, and TA? BTW, since you have access to a super accurate pH meter, why don't you get some tap water (presumably not acid like your pool) and test it at work, then use water from the same sample to calibrate your TFP meter?
Fair critique! It's supposed to be 100 today so I wanted one more day to swim and was just trying to see if I could easily enough raise the pH easily with two boxes of Borax and give the heater a break from the acidity for the last few days (albeit it's been dealing with it all summer!). You're on track with my next steps though.
 

BaileysBrew

Member
Aug 4, 2021
15
Lincoln, NE
Ok, water replaced and my CYA is now at 43. However, our local supply of water is pretty high in TA. Here's my numbers this morning with a gallon of chlorine added last night and no other adjustments:

TC - 1.5
CH - 250-300
TA - 140
CYA - 43
pH - 7.4

Given this, to lower TA the pool math calculator suggests adding 32 oz Muriatic Acid to lower pH to 7.2, or 76 oz to get to 7.0. It suggests aerating to get pH back up. Do you agree with that approach? Should I shoot for 7.0?

After that's adjusted, then it appears I could try aeration and see what I get. My DIY aerator isn't the best. If it doesn't do the job, maybe go the Borax route to get pH back up a bit without impacting TA too much. Any insight is super appreciated.
 

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