Chlorine after a heavier than normal usage

[mizzamouse]

Hey, Guys,

I had a quick question about the best way to maintain the pool after a heavier than normal usage (13 swimmers vs. 4) The day started off with the following test results:

FC - 2.5 - (Added almost 4 cups of additional chlorine this morning)
CC - 0
PH - 7.8 (Added 20oz of muriatic acid this morning)
CH - 350
TA - 100
CYA - 70

As of a few minute ago, chlorine is coming in at 2PPM, and CC is just about .5ppm

Should I SLAM the pool after heavy usage every time, or should I simply just add enough chlorine to bring me up to my target? Since I was below .5PPM of CC tonight, I just added about a gallon of chlorine to help bring FC up a bit.

Advice is greatly appreciated. Thanks!

 

[chiefwej]

SLAM is a process that requires overnight chlorine loss testing and days of maintaining shock levels. I'm not sure that is required. I do think you should bring the chlorine level up above your normal target level. Anywhere between the normal level and shock level is safe to swim. With a CYA level of 70 your normal FC target should be between 8-10, and you should never allow the FC to drop below 5. Your shock level is 28. You should immediately bring your FC up between 10 and 28. (I would recommend closer to the 28). Then never allow it to get below 5 again.

In the future, when you expect high bather load, bump the FC up near the shock level before the event, then once again after.

See this chart:
Pool School - Chlorine / CYA Chart

 

[woodyp]

If heavy use is expected.......raise your FC BEFORE the activities begin!

 

[mknauss]

I would also suggest that when you replace your SWCG you install an IC40. The IC20 you have is undersized. With an IC40, you should not have to add liquid chlorine unless you have a problem or a bunch of OPK (other peoples kids) swim in your pool.

Take care.

 

[mizzamouse]

Thanks, @mknauss!

I've heard from others that the IC20 is undersized. I brought this up to my pool builder, and they told me that it's rated for pools up to 20k gallons (which mine is below.) I've been recording my FC levels the past few days, and even with minimal use, I'm finding I need to add a decent amount of chlorine. As an example, here are my readings over the weekend: FYI - The pump runs 14 hours and the IC 20 set to 60%

Saturday morning: 9 swimmers.
FC - 7
CC - 0

Saturday Night:

FC - 4.5
CC - Little less than .5
I added 1/2 gallon of 12% chlorine

Sunday morning: (not that sunny, only 1 swimmer)

FC - 6.5
CC - 0

Monday morning: (Added about 48oz of chlorine)
FC - 4
CC- 0


Do you think I should bump the percentage on the IC 20 to produce more chlorine? Is there any documentation I can point my builder to that shows the IC 20 being undersized to try to swap for an IC 40?

Thanks for your help

 

[mknauss]

Your pool builder is right -- it is sized for a 20000 gallon pool if run 24 hours per day at 100% setting!!!!

So -- that is what you need to do to get the max chlorine out of the IC20. Your choice. Add bleach daily or up the run time and percentage.

Take care.

 

[mizzamouse]

Thanks again, @MKNAUSS!

I think the builder is saying the IC20 is sized properly because they are saying to keep FC between 1-3ppm. At 60% for 12hours a day, that should produce 1.44PPM.

In my situation, I want to maintain between 3-5PPM (More like 7ppm to keep a target of 5pPM) . If I manually added chlorine to bring me to 5PPM, and then set the IC20 at 80% for 12hours, that should produce 1.92PPM hopefully keeping me at or near my target.

Is my math off?

 

[mknauss]

They say it is properly sized because Pentair says that. It will create 0.7 lb of chlorine gas or about 4 ppm FC per 24 hour period in your pool size. That is just enough to combat sunlight loss at a CYA of 60-80 during the height of summer.

So if you are lucky and you can always only have a loss of 2 ppm, then you can run it at the time frame you state. As you get later in the summer and you have essentially a zero bather load, it should work.

Take care.

Keep in your memory that when this cell needs to be replaced, to buy an IC40. The power center will work with that size, and you will be able to run your pump a lot less and save $$ on electricity.