Where oh where is the Cl going?

GDK

Member
Jun 8, 2020
9
Glen Burnie, MD
Hello everyone,

I’ve owned my plaster pool for 26 years now and this has been my worst season ever getting things set correctly. I live in Maryland and uncovered in mid-May, late for us as it was rainy and cold. I heat with a solar cover so I need good sunny days but the pool only gets about 6 hours of direct sunlight a day.

Up to a week ago, I used Trichloro 90% tablets but have now stopped and converted to 12.5% liquid chlorine exclusively.

So, about 2 weeks ago, according to the pool store, my TA (221) and CYA (151) were way off and I started with adjusting the TA using muriatic acid and aeration. I then moved on to the CYA and drained about 40% of my water and refilled.

I had ordered a TFT100 test kit which arrived on 6/29 and I’ve included all the tests I’ve taken to date. I know the CYA is still high but having dumped about 40% last week and refilling with cold water, it came down but we are approaching our hot season here and I’d like to use the pool and another 40% drain and refill will kill my water temp. Besides, we will get plenty of rain in the next few weeks so I will undoubtedly be pumping it down.

6/29
pH 6.9
FC 1.0
CC 1.5
TA 100
CYA 110 (reading taken after draining about 30% so I drained a bit more)

6/30
pH 7.2
FC 1.5
CC 1.0
CH 400
TA 100
CYA 87

I threw in a couple bags of Power Power Plus 73 to add Cl and bring up the CH, however the next day:

7/3
pH 7.1
FC 0.5
CC 1.0
CH 500
TA 90
CYA 85

After this reading, I did a small “slam” not wanting to over chlorinate the pool because we want to use it on the fourth. So, I dumped in 2 gallons of LC, with the pump running and took a reading a couple hours later. The pool was in complete shade during this time. I got:

FC 16
CC 1.0
I waited 4 more hours and measured again:
FC 8.5
CC 3.0

This morning, 12 hours later, I did a full test:

7/4
pH 7.0
FC 2.0
CC 1.0
CH 525
TA 90
CYA 92

So the TA is still a bit high as is the CYA while the pH is low but I’ll aerate it to bring it up. My question is, where is my chlorine going? I appreciate your help and thanks in advance.

Gary
 

GDK

Member
Jun 8, 2020
9
Glen Burnie, MD
I'll drain some water this week to get the CYA down to acceptable limits then get balance and do a slam. I'll update everyone next week as to my progress. Thanks for the inputs.
Gary
 

GDK

Member
Jun 8, 2020
9
Glen Burnie, MD
Here's an update as to what I've done. I drained a significant amount of water and refilled to lower the CYA. Then two nights ago, we got 2.9" of rain so I drained again. I also opened the filter and cleaned off the grids, removing some tree seed debris in the process.
Last evening, I gave it a healthy dose of LC to get the FC up so I could do an Overnight Chlorine Loss Test. Test numbers last evening were:

pH 7.6
FC 7.5
CC 1.0
CH 375
TA 70
CYA 45

The pump was not running overnight and after it ran for an hour this morning, and before any direct sun, the FC has dropped to 4.0 (reduction of 3.5ppm) and the CC dropped to 0.5. So I guess a SLAM is in order? Reading the Chlorine/CYA chart, I should go for an FC of about 18, right?

I have 2 questions:
  1. Is it safe to enter the pool with this high level of FC? and if not,
  2. At would level would it be safe to do so?
Thanks
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,549
Laughlin, NV
Follow the SLAM Process. CYA of 50 ppm (round up)

You can safely swim in a pool as long as the FC is above the minimum and at or below SLAM level based on your CYA. You must also be able to see the bottom of the pool in the deep end of the pool.
 

GDK

Member
Jun 8, 2020
9
Glen Burnie, MD
It has been a week since my last post and this is what I’ve been doing. I drained lots of water and refilled and I also had to remove some rain water. My pump is on continuously with the speed adjusted for a 1.5 turnover in 24 hours. The water has been completely clear throughout this process.

On Friday morning, 7/10, I measured:
pH 7.4, FC 5.0, CC 1.0, CH 350, TA 80, and CYA 55​

I slammed it up to 22. That evening, I measured FC at 18.5 and CC at 1.0. I did not add LC and used these figures as a baseline for an Overnight Chlorine Loss Test.

The next morning, Saturday 7/11, I measured: FC – 10 and CC – 1.0 and I slammed up to 22. That evening I measured: FC – 15 and CC – 0.5 but I did not add any LC that evening and don’t recall why.

On Sunday morning, 7/12, I measured FC – 11.5 and CC – 0.5 and slammed again up to 22. Then Sunday evening I measured FC – 13.0 and CC – 0.5. Again, I don’t recall why but, that evening, I only slammed to 18.

One thing happened on Sunday. I had felt some slime on the underside of the step ladder on Saturday so on Sunday, I removed the ladder and found gobs of black, green and pink on all 3 steps. I removed the treads, brushed them off and gave them an extremely heavy dose of shock in a bucket of water. An hour later, they were completely clean.​

On Monday morning, I measured: FC – 13 and CC – 0.5 and slammed again up to 20. Then that evening I measured FC – 11 and CC – 0.5 and I slammed up to 20.

On Tuesday morning I measured: FC – 15.5 and CC – 1.0 and slammed again up to 20. That evening I measured:
FC – 16 and CC – 1.0 and realizing that I had not been good with the slam levels the past couple days, I slammed up to 23.5.

This morning, 7/15, performed a full test profile and measured:
pH 7.2, FC 19.5, CC 2.5, CH 350 TA 80 an CYA 50 I then slammed up to 22 this morning.​

As I stated earlier, the water has been completely clear throughout this process and I realize that I’ve not been prudent with keeping the FC level at the SLAM level. I gotta work on that.

Man, this process eats up the LC!
 

GDK

Member
Jun 8, 2020
9
Glen Burnie, MD
Oh, one more thing. In the spring, I'd bought some phosphate lowering liquid. I know it's not a TFP recommended item but does anyone see any issue if I just use it up to get it out of the chem box?