Does this seem right?

[Philo]

I have a Pentair IC60 SWG.
The SWG is set at 100% for 24 hours.
The pool is 30,000 gallons.
My CYA is 80.
The weather is hot. Between 85-95 degrees.

***I am having to add a gallon of Chlorine 2x per week to stay above 6ppm.****

Does this seem right?

Thanks

 

[YippeeSkippy]

If you have some contaminates in there, such as a child peeing in the pool or some occult algae developing you sure might.

Can you perform an OCLT (Overnight Chlorine Loss Test) to determine if there is something in the water chewing up your FC? Overnight Chlorine Loss Test

How old is your SWG?

Yippee

 

[Philo]

I'll check OCLT tonight.
SWG is 4 months old.
No one using the pool.

Thanks

 

[YippeeSkippy]

How are you testing your levels?? Do you have one of the two test kits we trust and recommend? The TF-100 or the Taylor K-2006.

How does your water look? Is your filter pressure rising as if its collecting something?

 

[Philo]

Water is VERY clear.
Filter Pressure is 10psi.
Yes on test kit.
FC 8
pH 7.8
Calcium 230
TA 90
CYA 70-80
Salt 3800

 

[JoyfulNoise]

An IC60 generates 2lbs of chlorine gas per day. In a 30,000 gallon pool, that equates to roughly 8ppm FC / day. Normal daily FC loss can range from 2-4ppm per day. So even at the high loss end your SWG should be keeping the 6ppm in place.

So if you are unable to maintain 6ppm and you are having to add additional chlorine every couple of days, then that means you are losing more than 8ppm FC in 24 hours.

I'll wager a guess that your OCLT is going to show an 8-hour over night loss of somewhere around 2-3ppm. But that's just a guess.

 

[Philo]

What you say makes perfect sense.
I'll check tonight.

Is there a chance that even though all the lights are green and it's at 100%, it's not making what's designed to make?

P.S. All the plates inside the SWG look new and shiny.

 

[Philo]

OCLT:
Last Night FC was 7.4
This Morning FC is 7.0

 

[JoyfulNoise]

Very interesting.

Ok, simple question - you turned off the pump and the SWG during the OCLT, right?

To answer your previous question - a 4 month old cell with clean plates should generate the as-spec'd amount of chlorine. It would be a rare circumstance that the cell is somehow underperforming. Unfortunately the only way to check a cell is to bring it to a pool store that has the equipment to check Pentair cells. There is a special wand needed (yes, it's called an IntelliWand) to connect a laptop to the cell wirelessly (it's uses a proprietary RF signal) in order to readout volts, amps, cell temp, etc. It's really one of the more annoying design features of Pentair SWGs. An authorized service center can do those checks.

As long as you are seeing little gas bubbles at your returns from the cell running, you can assume it's generating the rated amount of chlorine. You can use a clean water bottle to collect a water sample directly from the return and the FC should measure very high. Hard to say how much it will be but it should be a lot higher than the pool water.

 

[Philo]

Yes, I remembered to turn off the SWG.
Odd, I have never seen any bubbles coming from my return jets.

 

[pooldv]

Not everyone does. I think it depends on the plumbing. Some plumbing seems to accumulate it more and give a bigger bubble occasionally and some not at all. Mine is a nearly steady stream of tiny bubbles from the return closest to the pump.

 

[JoyfulNoise]

So let's just recap what's going here. You say that in order to maintain 6ppm FC everyday, you need to run your SWG at 100% for 24 hours per day. You are also adding 2 gallons of chlorine bleach as a supplement. So here's your FC input -

SWG @ 100% 24x7 --> 8ppm FC per day --> 56ppm FC per week

2 gal (256 oz) of 10% LC --> ~6ppm FC per week

So, in one week, you are adding 62ppm FC to your pool. Assuming worst case scenario FC loss at 4ppm/day, then your should lose about 28ppm per week. So that means you have an additional FC demand of -

62ppm - 28ppm = 34ppm/week = 4.85ppm per day = 0.2ppm per hour

Assuming you did an OCLT of 8 hours, one would have expected a 1.6ppm overnight loss but you only measured 0.4ppm. However, your weekly consumption rate of FC is more than DOUBLE what one would normally expect (62/28 = 220%) for a 30,000 gallon pool.

SO there's only two choices - your cell is bad OR there is something consuming a lot of FC during the day (no idea what that could be). Your options are - take your cell to a pool store and ask them to test the output as well as the voltage and current levels (ask if they can specifically test Pentair cells) and/or SLAM your pool anyway (it should be short) and see if the excess demand goes away.

I wish it could be more definitive but it really is a mystery that your weekly loss rate is so high but your overnight loss is normal.

 

[Philo]

Thanks Matt
I'll take it in to get tested.