Pool Not Holding Chlorine for SLAM

[GBRPool]

Hi all,

Thanks for having me here, reading the forums has so far been very helpful, and I'm hoping you can help me figure out my recent issue.

Backstory: About six weeks ago I inherited a 20k in-ground vinyl liner pool. The previous owner had taken great care of it, the only issue that I discovered was that the CYA was at about 100 when I took over. Probably from using exclusively stabilized chlorine tablets. Everything else looked good level-wise. I decided to continue to use the previous owner's method of adding stabilized chlorine tabs to the skimmer - not my ideal situation, but I figured I'd use up the chemicals and methods he left behind until the end of the short (Minnesota) season. This worked perfectly for five weeks, other than CYA remaining high. Until last weekend.

Background: Last weekend, I left town Friday-Sunday, and when I uncovered the pool on Sunday, it was cloudy blue. I couldn't see the bottom of the 3.5 foot shallow end. I had thrown a couple of chlorine tablets in the skimmer before I left, so something went completely crazy consuming chlorine. My test results were fine, except there was 0 FC and 0 CYA. After reading up on the forum, I supposed that the CYA had metabolized in the absence of chlorine. That's my hypothesis anyway, I'm curious if anyone has any other ideas for how CYA could completely disappear in, say two weeks (I stopped checking CYA as regularly as others after I saw it was so high and assumed there was no way to lower it except over a long time or via refill).

So, SLAM time. My issue is that the pool just will not hold chlorine for long enough to reach SLAM levels, let alone maintain them. I started by adding liquid chlorine just to get some chlorine in the pool to help prevent further growth. I also added 5lb stabilizer so I had some CYA to hold the chlorine I was adding. After about a day, I started to see CYA readings, so I assumed it was distributing and I started the SLAM for real, adding four gallons of LC to reach the recommended 10 FC SLAM level. From the start, adding four gallons didn't result in the expected rise in FC. At first, it would put me at about 2 FC. By the end of day one, I could get to six or seven FC, but in the morning it was always back to 0-0.5. I ended up dumping so much liquid chlorine in the pool over days one and two that I needed to change tactics - something wasn't working.

I thought that maybe the liquid chlorine was weak. It was from Home Depot, and the batch numbers indicate that it was made in March, so totally plausible. I also took my water in to a pool store. The levels were within range, other than 0.46 FC and 2.66 CC. They recommended a partial refill to reduce 2350 TDS, then adding 10 bags of Bioguard Burnout 3 granular shock. After reading up, I disregarded the partial refill. As I suspected the LC I could get my hands on was weak, I decided to jump straight to shock.

Last night, I added 8 lb of 53% Hypo Cal granular shock to get to the CC break even point and start the SLAm. My FC reading about 10 minutes after adding was 12 - far lower than what I expected. But I had to go to bed, so I hoped it was still circulating and would rise. This morning, FC is back to zero. Eight pounds of shock gone overnight.

So I don't know what to do. What's preventing chlorine from taking hold in my pool? Things I haven't yet tried but am considering - cleaning cartridge filter (had to wait for stabilizer to be fully distributed), any kind of algaecide, floc, chemicals other than chlorine, partial refill (gulp). Phosphate reading from pool store test was 2308, but they didn't say anything about that and I don't know enough about phosphates.

Here are my current levels:
FC - 0-0.5
CC - 2.2
PH - 7.0
TA - 129
CH - 171
CYA - 36 (from yesterday, I ran out of testing solution, so I'm sure it's higher after adding shock)

Edited to add: I have seen some progress, as I can now see the bottom of the pool in the 4.5-foot "deep" end. The water is still very cloudy.

 

[wireform]

What testing method are you using leaving the store out of the picture.

 

[GBRPool]

TF-Pro

 

[Texas Splash]

Welcome to TFP! Since you have a TF-Pro, there is no reason you can't get the water fixed, but to this point you haven't really been doing the SLAM Process properly. In the early part of the SLAM Process, you have to increase the FC quickly and remain vigilant to test again and maintain the FC as needed. The first day you might need to test again in 30 minutes or an hour until the FC stabilizes. You mentioned running out of the CYA R-0013 reagent, so if that number above is from the pool store, disregard it. You must test your own CYA to start the SLAM Process. No guesswork here. The proper FC SLAM level depends on an accurate CYA.

 

[GBRPool]

I hear you, the CYA reagent is on the way. The problem is the "raising the FC quickly" part. Dumping 4 gallons of liquid chlorine should get me to 20 ppm, but only got me to six. Eleven pounds of hypo cal (said 8 in my original post, realized it was actually 11) should have gotten me to 36 ppm FC, but only yielded 12 initially, down to zero overnight. I will try liquid bleach today and see how it goes.

 

[mknauss]

If the CYA went to 0 that quickly, that implies bacterial destruction which creates ammonia. You likely have defeated that as the pool is holding some FC after 30 minutes. The CC of 2 and pH of 7 implies that you had ammonia and it should be pretty much gone. Now follow the normal SLAM process.

 

[Texas Splash]

Dumping 4 gallons of liquid chlorine should get me to 20 ppm, but only got me to six.

Agreed, that is a very large disparity. Hard to believe the chlorine is that weak. I would avoid the cal-hypo for the SLAM if you can. In some of your description I feared your pool might have converted the previous stabilizer to ammonia which might also explain why your pH was on the low side. But with ammonia your water will consume any stabilizer and FC very fast. Not sure if your water is in some sort of transition like that, but once you get the CYA reagent, please confirm the CYA and post back. I suspect you'll end-up adding 10 ppm worth of FC at first when you re-start the SLAM, then test the FC in 10 minutes (no longer) with good circulation and a quick brushing. Then add chlorine/bleach again and repeat as necessary to ensure the FC stays somewhere between 6-10 ppm for at least 10 minutes BEFORE adding any more stabilizer.

Once you are sure the FC is showing signs of holding, only then add stabilizer for a CYA goal of 30 (if needed) and maintain an FC of 12. All of this assuming your CYA is much lower than you expect, but we'll see once you are able to test.

 

[GBRPool]

Awesome info, thank you all. I will report back when I get CYA levels and restart.