Trying to figure out what to do first - CYA high, Ph a little high, FC low

S. Isaacs

Member
Sep 6, 2020
5
Phoenix, AZ
Thank you everyone in advance for your time and advice. I took over 5 weeks ago for the first time from our pool guy.
These are the test results:
FC 0.5
CC 0.5 or 1
Ph 7.8
CYA over 100 - I guess my pool guy has been using tons of chlorine?
These two I haven't done in a couple of weeks, but I can test again if that is helpful
Ch 750
Ta 120

When I saw the high CYA level, based on the Pool School TFP eBook, I emptied half the the pool then refilled with tap water. While I was figuring out how to empty it, the water turned light green so I've been pouring in a bottle of bleach every couple of days and it's been staying clear, but FC remains low. CYA, even after refilling, remains over 100 which is confusing me.
The water is basically clear - it may have a very slight green tinge, but I am not sure.

What should I do next?
Figure out how to lower the CYA? Then shock?
Shock it without lowering it?
Do I need to lower the Ph or anything else?

Thanks!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,301
Laughlin, NV
Welcome to the forum!
You will need to drain again. Before you do, do the following.
100 is the limit of the CYA test, so you have to do a diluted test. Mix 50% pool water with 50% tap water. Use this mixed sample as your test water. Multiply the result by 2 for your CYA level.
Is the CH level you show before or after your drain/refill?
I suggest you read ABC's of Pool Water Chemistry.
 

S. Isaacs

Member
Sep 6, 2020
5
Phoenix, AZ
Thanks so much for the welcome and your message.
I tested the CYA again twice:
After mixing 1 part pool water and 1 part tap, CYA 75
After mixing 1 part pool water, 2 parts tap water, CYA was between 40-50
So should I empty 2/3 of the pool?
I measured the CH, it is now between 450 and 475
When I empty and refill it, it sounds like I may have to increase the calcium level.
Thanks again.

Welcome to the forum!
You will need to drain again. Before you do, do the following.
100 is the limit of the CYA test, so you have to do a diluted test. Mix 50% pool water with 50% tap water. Use this mixed sample as your test water. Multiply the result by 2 for your CYA level.
Is the CH level you show before or after your drain/refill?
I suggest you read ABC's of Pool Water Chemistry.
 

Msch99

Gold Supporter
Bronze Supporter
Jun 11, 2018
906
Verona, MO
Use 80 as your CYA. Always use next highest number if in between lines.
I would use 40 as your CYA goal, so another 50% exchange is needed.
You will most likely need to “slam” after the exchange. See link in my signature for explanation. Slamming is different than your traditional “shocking”.
Once you have exchanged water, run a full set of tests and post here. The experts will assist on what your next steps should be.
Welcome to TFP! 😀
 

red-beard

Gold Supporter
May 27, 2019
587
Houston, TX
CYA being extremely high is common and is usually caused by use of Trichlor tablets. I used them for years. I believe I was nearing 1000 ppm CYA after 7 years! I drained my pool again this year and was able to get my CYA fully under control. I have not SLAMed since.

I know that draining and refilling is a pain, but it really helps. Do not worry if you drain too much, as it is easy to get the levels back into place. 30 is a really good target since it allows slamming with lower levels of Chlorine. 40 is also a good level.

Since you will need to raise calcium after refilling, you may wish to chlorinate with Calcium Hypo Chlorite powder. This is what I did this year. Switch to liquid chlorine (bleach) after the CH level is 350.

Once your SLAM is finished, you may use some trichlor tabs you probably have laying around to raise your CYA to 40-50.

As you are refilling, start adding bleach to the water. Test as soon as you are full. Then follow the regular SLAM process.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,301
Laughlin, NV
After mixing 1 part pool water and 1 part tap, CYA 75
That puts your CYA level now around 150-160. Target of 50 ppm or less. So a 3/4 drain and refill is needed.
I measured the CH, it is now between 450 and 475
Great. Your fill water CH is most likely around 250 ppm. (Test your fill water CH and TA and record that). So your CH will be fine after you do the next drain/refill.
Weather is cooling and sun angle is dropping so it is becoming safer to drain the pool now.
 

S. Isaacs

Member
Sep 6, 2020
5
Phoenix, AZ
Thanks again for all of the helpful feedback.
OK so I emptied and filled about 3/4 of the pool, and here are the current results. I haven't added anything yet.

Ph 8.2
FC 0.5
CC 0.5
CH 275
TA 160-170
CYA 40

I also tested my tap water:
CH 150
TA 120-130

What's next?
 

Msch99

Gold Supporter
Bronze Supporter
Jun 11, 2018
906
Verona, MO
Chlorine! 😀
Maintain 5-7ppm normal conditions.
Lower PH to 7.2 or so with muriatic acid, which will lower your TA a bit too.
16ppm for slam.
 

red-beard

Gold Supporter
May 27, 2019
587
Houston, TX
If your water is clear, I would increase FC to 7 ppm & add enough Muriatic acid to bring the pH down to at least 7.5. Use Poolmath for your additions. Keep the pump running and brush the pool walls. After 1 hour, check your FC again. I would do this in the evening and then check FC in the morning for an OCLT (Overnight Chlorine Loss Test)
Overnight Chlorine Loss Test
If you lose less than 1 ppm FC over night, your water is clear and your CC 0.5 or less, you are good to go! Check your FC each evening and make your add each night once you are finished swimming.

If you fail the OCLT, you should SLAM

SLAM Process

You need to work on lowering your TA down to 60-80. Here is how!


Eventually, you should work on increasing your Calcium Hardness (CH) to at least 350, but this can be done later. You are above 250, so you're in the ball park. With your tap water, eventually your CH may go up to 350 with just water additions from evaporation.
 

S. Isaacs

Member
Sep 6, 2020
5
Phoenix, AZ
I added the muriatic acid and the PH is down to 7.5 now. Is there a benefit to go lower?
OCLT failed, so I am SLAMming
Thanks

If your water is clear, I would increase FC to 7 ppm & add enough Muriatic acid to bring the pH down to at least 7.5. Use Poolmath for your additions. Keep the pump running and brush the pool walls. After 1 hour, check your FC again. I would do this in the evening and then check FC in the morning for an OCLT (Overnight Chlorine Loss Test)
Overnight Chlorine Loss Test
If you lose less than 1 ppm FC over night, your water is clear and your CC 0.5 or less, you are good to go! Check your FC each evening and make your add each night once you are finished swimming.

If you fail the OCLT, you should SLAM

SLAM Process

You need to work on lowering your TA down to 60-80. Here is how!


Eventually, you should work on increasing your Calcium Hardness (CH) to at least 350, but this can be done later. You are above 250, so you're in the ball park. With your tap water, eventually your CH may go up to 350 with just water additions from evaporation.
 

JJ_Tex

Bronze Supporter
Jul 17, 2019
1,723
Prosper, TX (DFW)
I would add acid to bring it down to 7.2, 30 mins later bring your FC up to SLAM level and keep it at that level by testing and adding multiple times per day, and only end when you pass the criteria to end the SLAM.