Chlorine dropping with SWG

[rickjr82]

I just took over pool maintenance in July (new pool opened in mid May) been working to lower TA - MA is the only thing I've been adding (~3 gallons this month so far).


The SWG (IC 40) had been running at 20% as I was trying to lower my chlorine from 10-12 to about 6ppm.
Last test on Wednesday, I showed it at 5ppm - so I bumped it back up to 40%, on Wednesday it was 4.5, so I bumped it to 60% . It's now showing at 2.5ppm today. CYA is 90.

Pool math says to run it at 14% for 1.5 hours. Doesn't seem like that would help.

Salt levels seem fine - 4000 and green on the IC40.

I've used both the TF100 test as well as some strips left by the builder - test results seem consistent.

Any ideas why FC keeps dropping?

Could rain have that much of an effect? We're in NE Florida (Jacksonville).

 

[mknauss]

Welcome to the forum!

You need to be running your SWCG at 100% for 12 hours per day, minimum. That adds right at 4 ppm FC per day in your pool.
At a CYA of 90, you should not go below 5 ppm and best to stay at or above 7 ppm FC.
I suggest you read ABC's of Pool Water Chemistry.

 

[rickjr82]

Welcome to the forum!

You need to be running your SWCG at 100% for 12 hours per day, minimum. That adds right at 4 ppm FC per day in your pool.
At a CYA of 90, you should not go below 5 ppm and best to stay at or above 7 ppm FC.
I suggest you read ABC's of Pool Water Chemistry.

I've adjusted the to 100% for the last 2 days - today my FC is even lower (at 2).

I've read it through the ABC's a couple times before posting this (as well as the rest of the pool school), not sure what I'm missing.

 

[mknauss]

If running the SWCG at that level does not maintain your FC, I suspect you have algae. Do a Overnight Chlorine Loss Test tonight.

 

[HeyEng]

I've adjusted the to 100% for the last 2 days - today my FC is even lower (at 2).

I've read it through the ABC's a couple times before posting this (as well as the rest of the pool school), not sure what I'm missing.

How long are you running it at 100%?

 

[rickjr82]

How long are you running it at 100%?

All day - I haven't touched it since setting it last. Unless I'm missing a way to adjust run time.

 

[HeyEng]

All day - I haven't touched it since setting it last. Unless I'm missing a way to adjust run time.

Then I agree w/ mknauss...very likely you have algae.

 

[jimbethesda]

All day - I haven't touched it since setting it last. Unless I'm missing a way to adjust run time.

"All day" = 24 hrs/day? Numbers are best when posting information here.

"it" should also mean your pump. How many hours a day does your pump run?

 

[rickjr82]

Pump runs 18 hours a day.

I just ran the OCLT and went from 5 to 1.5 overnight. I bought 10 gallons of 10% bleach and I'm going to start the SLAM today.

I'm not planning to try and lower the CYA first b/c it seems like a lot of draining to get it down to 60 or so (even though it's going to be more chlorine).

I've lowered the PH to 7.2 and will start adding bleach shortly.

 

[Dtkokay]

Good luck! For your CYA level, keep in mind that 70 or 80 is actually the recommended level with a SWG, not 60, so you’re actually just a little over the recommendation. Yes, you’ll use up more chlorine during the SLAM, but no need to drain to lower the CYA to 60.

 

[SouthVirginiaPool]

Good luck! For your CYA level, keep in mind that 70 or 80 is actually the recommended level with a SWG, not 60, so you’re actually just a little over the recommendation. Yes, you’ll use up more chlorine during the SLAM, but no need to drain to lower the CYA to 60.

I've seen that on the Chlorine/CYA tables too. Does anyone know why 60 ppm of CYA is suboptimal for a SWG pool? My pool is currently at 60 CYA, and I run the SWG at 75% x 12 hours and it keep the FC pretty steady at 5.5 - 6 ppm. Don't think I'll hurt anything by being too low on CYA. Just curious to the reasoning. I'll be adding CYA soon anyway as it has likely been creeping down due to rains and splash out.

 

[mknauss]

Don't think I'll hurt anything by being too low on CYA. Just curious to the reasoning.

Each climate impacts how much CYA is needed to keep the FC loss minimalized for a pool system. If my CYA drops below 70, my FC loss goes up dramatically. If you can have lower CYA but no gain in FC loss, and no drop in FC to below mimimum during the time of high UV loss (afternoon), then do what your pool needs.

 

[rickjr82]

OK, I shut off my SWG and put in 6 gallons of 10% in the morning (7am). I checked every 4 hours or so and kept my FC at 35ppm. By 5pm the water was clear (we noticed some cloudiness the previous night after my posts).

I ran the OCLT with a starting FC of 39 @10:45pm (I guess I put in too much bleach on my last add @8pm) and it was 39 this morning @6:45am (no loss).

From what I understand, we are good now:
0 CC
Clear water
0 loss in OCLT

Is a 1 day SLAM something that can happen, or did I mess up somewhere?

My plan now is to monitor the chlorine and turn back on the SWG when it gets to about 15ppm and aim to keep it around 8ppm (assuming my CYA stays at 90). I will then clean out my filter.

I appreciate everyone's help on this.

 

[mknauss]

You got on it fast and monitored it closely. Follow your plan and see how it goes.

 

[Dtkokay]

I have my fingers crossed for you. Maybe do another OCLT test in a week as a sanity check, but it sounds like you’re headed in the right direction.

 

[rickjr82]

Looks like everything is good now!

FC: 10.5
CC .5

my CC's were 1.5 a day after I completed SLAM, but then I followed mknauss's advice from another thread and cleaned out my test tubes with bleach and it went back down to .5. Will be cleaning out the filter tomorrow.