Newbie trying to balance chlorine

[snuggler]

Good afternoon everyone,

We moved into a house with a ~23,000 gallon chlorine inground pool that had been (we are told) properly winterized by a professional. The cover was a safety cover that looked pretty solid, although I don't know the difference between what a mesh v. non-mesh cover looks like yet.

We had a professional open it this past Friday, and everything seemed to go ok. He said he shocked it, and I saw him brush and vacuum and do all the other things I expected him to do. I was told to turn off the hose after a few hours because the water level was low, and to backwash the filter when the pressure went up, which he expected would happen in a day or two as the filter cleaned all the gunk out.

I forgot to turn the water off until the next day, so the water level is high now; just over the top of the skimmer. We also had an unfortunate mouse hop in the pool and drown overnight, before I could get our "frog logs" in.

I tried to balance the chlorine level yesterday but didn't have much luck. I bought liquid chlorine (12%) and added the amount I was told to add via the Pool Math app (158 ounces) for my CYA level (60) for a target FC of 7. I checked the FC level again about 4-5 hours later and the FC level didn't get anywhere near 7. It started at 0.6 FC, and only went up to 1.2 FC.

I tested for CC as well, and got a high reading--3.5. But I know I have MPS shock in my shed, and think my pool guy may have used it to shock the pool when it was opened. I am going to try to find the reagent for this so I can account for it with my CC testing (via a Taylor kit), but I won't be able to do that until tomorrow. My pH was 7.4 when I added the chlorine.

Additionally, it was an extremely hot day yesterday (95 degrees).

Thoughts on what I should do next? Should I try to balance the FC again tonight when I get home for work? Or should I wait until tomorrow when I can (hopefully) find the reagent to see if I have an actual CC problem or just an issue with MPS affecting my CC testing? Should I start the SLAM process from scratch tomorrow?

Is it possible the high heat, recent opening, likely reduced skimmer operability due to high water level, or dead mouse made my pool use up that much chlorine quickly but there isn't a general problem with my pool? Anything I should focus on immediately before tomorrow, when I plan to re-test with the MPS-blocking reagent, backwash my filter and lower water levels, add more chlorine, skim, and put in a robotic vacuum? I have very limited time today due to a full-time job and a really sick kiddo, but I can probably find about 20-45 minutes to take care of the pool late tonight.

 

[magiteck]

My immediate concern would be the low FC, not the CC reading.

Here’s what I would do tonight:
Pump running. Test. Add enough LC to bring the pool to SLAM level. Wait 10 minutes, and test again. Make sure the FC actually went up and get that baseline level.

Then if you can, test enough in the morning to see what you’ve lost. If you lose more than 1ppm overnight, its SLAM Process time.

If your FC doesn’t go up for some reason after the 10 minute test, then we might be looking at bad LC or an ammonia issue.

 

[snuggler]

My immediate concern would be the low FC, not the CC reading.

Here’s what I would do tonight:
Pump running. Test. Add enough LC to bring the pool to SLAM level. Wait 10 minutes, and test again. Make sure the FC actually went up and get that baseline level.

Then if you can, test enough in the morning to see what you’ve lost. If you lose more than 1ppm overnight, its SLAM Process time.

If your FC doesn’t go up for some reason after the 10 minute test, then we might be looking at bad LC or an ammonia issue.

Thanks. I added enough chlorine to bring my pool to SLAM level and the FC level went up appropriately after 20 minutes.

I tested again in the morning but not until late morning (11 am, so about 12 hours later). (Sick kiddo thwarted my early morning testing plans). I ran out of the appropriate reagent, but the water was getting close to changing to clear as I ran out of reagent. Assuming I only needed another drop or two to get to clear, I would have lost about 3-4 ppm of FC. I haven't tested again yet because I'm waiting for my new reagent to arrive on Thursday. I couldn't find anyone locally who sells it.

Water is crystal clear and looks amazing now that I lowered the water level to allow the skimmer to filter correctly, and now that I have a Dolphin cleaner helping me out.

Do I need to SLAM again and do an overnight chlorine loss test when I get the new reagents on Thursday? Or is the reduction of 3-4 FC after 12 hours that I saw yesterday acceptable? As a reminder, the whole reason I was worried was because my CC level was high at 3.5. But I think my pool guy did an MPS shock last Friday, so I'm not sure how to account for that as I know it can mess up the CC test.

And if I SLAM again on Thursday, can we swim on Friday if the overnight FC loss is 1 ppm or less? Or does the CC level need to be good as well? And does the FC level also need to drop down to maintenance levels (5-9 for my CYA of 60) before we can swim, or is SLAM level or less ok as long as the overnight chlorine loss is 1 ppm or less?

 

[IceShadow]

When you get the reagents, do an Overnight Chlorine Loss Test. It sounds like a drop that isn't expected, but with the sun on the pool in the morning, there's a lot of variables that could be affecting things. Gotta do it properly, add the FC after dark, test to give you a baseline, then test again before dawn to make sure there isn't an unexpecxted drop overnight.

If there is, you could be losing FC from whatever chemicals were used to open the pool, or it could be something living. If it's the former I expect the SLAM to be fast. If it's the latter it could depend on how quickly we find where the algae is growing and kill it.

If MPS was used then I'm not sure how the CC will be affected. I know MPS reads as CC on the test, so it may be just unreliable for you for CC until the MPS is gone.

The pool is safe to swim in if the pH is in the 7s, the FC is at SLAM level or below, and you can clearly see the bottom of the entire pool.

 

[snuggler]

When you get the reagents, do an Overnight Chlorine Loss Test. It sounds like a drop that isn't expected, but with the sun on the pool in the morning, there's a lot of variables that could be affecting things. Gotta do it properly, add the FC after dark, test to give you a baseline, then test again before dawn to make sure there isn't an unexpecxted drop overnight.

If there is, you could be losing FC from whatever chemicals were used to open the pool, or it could be something living. If it's the former I expect the SLAM to be fast. If it's the latter it could depend on how quickly we find where the algae is growing and kill it.

If MPS was used then I'm not sure how the CC will be affected. I know MPS reads as CC on the test, so it may be just unreliable for you for CC until the MPS is gone.

The pool is safe to swim in if the pH is in the 7s, the FC is at SLAM level or below, and you can clearly see the bottom of the entire pool.

Thanks, this is super helpful.

So, to confirm, it is safe to swim if pH is in the 7s, FC is SLAM or below, and I can clearly see the bottom of the entire pool, even if CC level is still high and even if I'm still in SLAM (e.g., because the overnight CC loss is still greater than 1 ppm?).

 

[IceShadow]

Yep. The CCs (if they are CCs and not MPS showing up as CCs) might cause some odor or eye irritation but it's not unsafe in and of itself.