No chlorine

[Johnklavanian]

Hey all. Having a terrible problem with 0 total and 0 free chlorine on test strip kit and also reagent kit. Other levels all normal range: pH 7.4, cya 40, total alkalinity 120.
42k gallon in ground granite pool. It all started with a green algae bloom approx 1 month ago. That resolved with a triple dose shock of liquid chlorine. In the past month I've shocked 5 times using liquid, granular cal hypo, and non chlorine shock. The pool is now clear and looks great. Still free chlorine reading 0 and has never gone up. Occasionally the total chlorine reading on the test strip will look like 1 ppm
Use a hayward auto chlorinator which I also replaced in case that was the problem.
Thanks for any ideas

 

[Texas Splash]

Welcome to TFP! The water may be clear but I don't think you're out of the woods yet. You need liquid chlorine and lots of it, but accurately dosed. Test strips are horrible. You really need a TF-100 or Taylor K-2006C test kit. With one of those, post a full set of results and we can walk you through a SLAM Process to remove that algae once and for all.

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[Johnklavanian]

Thanks!
Got the taylor test kit:
FAS/DPD: free chlorine 0; combined chlorine 0.4; total chlorine 0.4- this is with a new full autochlorinator using 3in pucks set to highest flow speed.
pH: 7.4
TA: 90
CA hardness: 440; saturation index 0.15
CYA;: 60

I had a pool company out and they said the sand in my filter needs to be replaced and got me on the schedule for that, not sure if it could be eating the chlorine. He had no suggestions about the chlorine.
Like I mentioned before, have tried 16 gallons of liquid chlorine shock twice (42k gallon pool) 12 lbs of hth chlorine shock, and 12lbs of non chlorine shock all multiple times over the past month. only one time did I ever have a detectable chlorine reading and that was 20ppm total chlorine but only for an afternoon then back down to 0.
pool still crystal clear. no significant discolorations on the floor, no clear algae contaminants that I can see. polaris vacuum runs daily. I am thinking of just closing the pool I'm at a loss! Thanks for your help.

 

[Texas Splash]

Okay, good job with your own test results. I can tell you this, the sand has nothing to do with your issue. It's all chemistry, not mechanical filtering. Don't waste your time or money changing the sand unless it was ruined before by adding floc or clarifier. Sand never goes bad otherwise.

Also do not use any other stabilized chlorinating products like tabs, bags of shock, etc. Your CYA of 60 is high enough. Liquid chlorine is the #1 item your water needs. Here's what you should do at the moment.
1 - Lower the pH to about 7.2 (muriatic acid)
2 - Increase the FC to 24. 24 is the approved FC SLAM level per the FC/CYA Levels based on your CYA. Use the PoolMath APP to confirm the dosage amount.

From that point, test the FC again in about 15 minutes with good water circulation. If it dropped significantly, increase it right away. Don't wait hours. Not right now anyways. With liquid chlorine on-hand and frequent testing, you should be able to break through the barrier that is preventing the chlorine from holding. You might have to test the water and add chlorine rather quickly for the first few times, then it should settle down and stabilizer (hold). Let us know.

Just to confirm .... no other odd store products added to the water other than what you noted above correct?

 

[PoolStored]

I had a pool company out and they said the sand in my filter needs to be replaced and got me on the schedule for that, not sure if it could be eating the chlorine. He had no suggestions about the chlorine.

Sand is millions of years old. No need to replace sand unless calcium levels or unnecessary chemicals have turned the sand to a solid block. *oh those pool companies...*

Like I mentioned before, have tried 16 gallons of liquid chlorine shock twice (42k gallon pool) 12 lbs of hth chlorine shock, and 12lbs of non chlorine shock all multiple times over the past month. only one time did I ever have a detectable chlorine reading and that was 20ppm total chlorine but only for an afternoon then back down to 0.
pool still crystal clear. no significant discolorations on the floor, no clear algae contaminants that I can see. polaris vacuum runs daily. I am thinking of just closing the pool I'm at a loss! Thanks for your help.

Read this and get going --> SLAM Process
Also, re-read this --> ABCs of Pool Water Chemistry

You can do this, it is not hard. When you are done and you are using Liquid Chlorine, or SWG, you pool will look like this and will take just a few minutes a day. Inspiration --> TFP Clear - Let's see PICs!