Chlorine Demand Problem with Salt Water Pool

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jkaba

jkaba

0
Jul 7, 2014
13
Hays, KS
I've been a pool owner for 20 years, but just switched to salt water this year. Only had Chlorine Demand issues a couple of times during those 20 years, and both times I drained my pool down and double or triple shocked my pool with Cal Hypo. Since I rarely had an issue the last few years, I let my guard down, and did not test my pool very often, and had my SWG set to 30%. I left town for a week in June, and returned to a cloudy pool. In the past I have relied heavily on the pool stores tests, and have bought a few of my chemicals there to keep them happy, however this year they are charging for the tests and are not very cooperative in that they refused to do a chlorine demand test for me. That is the only store in our town that does testing so I searched online and found this forum. I ordered the TF-100 test kit today, and am debating what steps to take in the meantime. Here are my numbers from water tests performed at the pool store.

6/26 - Came home and pool was cloudy. Could barely see bottom in 3 ft. area.
CYA: not tested
FC: 0
CC: .1
PH: 8.3
CH: 329
TA: 143
Actions taken: Acid to bring down TA and PH. Set SWG to Superchlorinate. Added a few ounces of clarifier. Added a half bottle of Algecide because of all the rain we had the week we were away.

6/30 - Clarity of water was better, but still not seeing bottom in deep end.
CYA: 103
FC: 0
CC: .1
PH: 7.3
CH: 365
TA: 109
Actions taken: 3 lbs Cal Hypo. then waited a few hrs, then 2 gal. bleach, and kept SWG set on Superchlorinate. Added more clarifier and SparkleUp(flocking agent) next day. Couple ounces of Algecide added.

7/2 - Can now see bottom of pool in the deep end, but water lacks clarity and luster(dull)
CYA: not tested
FC: 0
CC: .1
PH: 7.8
CH: 340
TA: 149
Phophates were tested and found to be 500
Actions taken : More acid to bring down TA and PH, and Put in 1 liter Phosfree. Shocked with 5 lbs Cal Hypo, waited a few hrs, then added couple more gallons of bleach, and SWG set to 100%.

Today - Water is clear, but each of the times we vacuumed the pool, we noticed a dirty film on the liner which may have been algae. Looks like a film of dirt. Not as much residue on the bottom as we have noticed from the previous few times, but still not holding chlorine. Noticed CYA really high, which probably explains why I haven't reached chlorine breakpoint?
CYA:131
FC: 0
CC: .1
PH: 8.1
CH: 339
TA: 154
They also gave me a Saturation index of .9 (haven't researched this to know what that is all about)
Actions taken: Added acid to bring down TA and PH. Now waiting to hear from all of you experienced people to give suggestions. Was thinking of a partial drain. Maybe 1/3 then shock with 10 gallons of bleach???? Any other suggestions ideas.
 
Welcome to TFP!

Your CYA is much too high, so you likely need to replace some water ... although verify with your TF-100 (great choice).

We never recommend adding an arbitrary amount of chlorine. Always test and use PoolMath. You will need to follow the SLAM process (see how to in Pool School) to clear up the pool using bleach, not the SWG. You should never need to use clarifier or algaecide.
 
That change is probably a testing problem. None of the available CYA tests are precise enough to distinguish those two levels from each other. Digital testers are especially deceptive, giving three digit results that are actually +-20 or worse.
 
It will make more sense to try the test by the instructions first. If you see you are at or around 100, add 50% tap water to your pool water, run the test again, then double the result. You may be well over 100. CYA tests get very unreliable when the content is over 100ppm. With a SWG, luckily you may not have to replace a whole lot of water, I'd shoot for 70ppm CYA.

Here's the issue, if CYA is sky high, you will almost positively not have enough FC in the water to keep it sanitary, and probably won't be able to maintain a very high FC with a SWG.
 
I was where you are about a month ago. My CYA was around 100 and I couldn't keep the pool clear. I had gotten lazy and used Trichlor pucks over the winter, resulting in my high CYA. The Pool Store kept telling me my Cl was high, yet I kept getting algae growth in between random shocks. I found TFP, lowered my CYA and was able to clear up the pool with a single night of SLAMming. I haven't looked back, keeping my daily doses of CL added to the pool until I installed my SWG 2 weeks ago. The takeaway from that was CYA=100+ is a back breaker. It was expensive to try to keep pace and it proved impossible without a good test kit and TFP. Stick with it, and you will get there too.
 

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Ok, I received my test kit yesterday and initial tests showed

CYA 80
FC 2.0
CC 1.5
TA 160
CH High(700) Source water is high(maybe 400)

I was concerned with the CYA at 80 and wanted to reduce it, so vacuumed algae and leaves to waste, and dropped it about 8", refilled, added salt, and a little acid(source water has a higher ph), tested again this morning and new results are:

CYA 70-80
FC 1.5
CC 1.5
TA 160
PH 7.2 -7.5 maybe 7.3? Using TF-100 kit, and color match scale jumps from 7.2-7.5 (reads closer to 7.2)

Planning on Slamming today using 9 gallons of 8.25% bleach as per Pool Math and the tables for the SWG shock for a CYA of 80. Does this sound like a good plan?
 
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