SWG can't keep up

[pfitz4]

I need help interpreting my test results and FC consumption. I've typically been able to keep the SWG around 40-50% and maintain more than adequate FC. I like to keep FC higher than the recommended level to give myself a buffer, aiming for FC of 5 or 6 with CYA of 70 (or at least 60).

Within the last two weeks, we had several inches of rain. I've kept the water level higher and haven't drained any water. CYA dropped to 50. FC is now hovering around 3.5 even after turning the SWG up from 50% to 75%. I set it to superchlorinate this morning to see how that will affect FC. It seems like 75% should be more than adequate for my pool, considering the salt cell is a bit oversized (T-15 is for 40,000 gallon pool and my pool is 25,000 gal.)

So, is the drop in FC just a result of the CYA getting diluted or dissipating? We've had normal bather loads and temps typical to past seasons. OCLT was fine.

Most recent test results:
FC 3.5
CC 0
CYA 50
TA 80
pH 7.5
Salt 3200
Pump running 10 hrs/day
Pool temp around 90 degrees

 

[ajw22]

How old is your cell?

When did you open the cell up and check for scale on the plates?

 

[SpringPool]

From the reading I’ve done I wouldn’t use boost it wears out the cell. Better to top off with liquid chlorine.

If I understand the cl/cya relationship correctly then yes if you have less cya in the pool then it can be consumed quicker since the cl that doesn’t bond to the cya is unprotected from the sun.

I would check the cell for scaling but also bump your cya back to 70 and see if that changes your output back to what you used to use. If it doesn’t depending on the cells age it might be going bad or needs to be cleaned.

 

[Jimrahbe]

p,

Your cell, if working ok, will increase your FC by 6.7 ppm in your pool when running at 100% 24/7. That is basically .28 ppm per hour.

Running for 10 hours gives you 2.8 ppm and if only running at 75% output then you are down to 2.1 ppm increase per day.

The lower your CYA, the more FC the pool will consume each day. Most pools use 2 to 4 ppm of FC per day.

If you have not inspected your cell lately, any build-up between the plates will drastically decrease the amount of chlorine it can make.

Thanks for posting,

Jim R.

 

[pfitz4]

Thanks for the information- very helpful.

I replaced my cell last month so it’s basically brand new.

So would you suggest increasing CYA?

 

[Jimrahbe]

p,

I would run the CYA at 70 or 80... and keep the FC in the proper relationship per this chart ... [FC/CYA][/FC/CYA]

I would also do two tests...

1. Run an Overnight Chlorine Loss Test... Overnight Chlorine Loss Test This just makes sure that nothing is in your water... (SWCG is off, of course)

2. Run the same test the next night, but this time with the SWCG on 100% and the pump on all night. The increase in your FC level will tell you how much chlorine your SWCG is making per hour.. This test just proves how well you SWCG is working.

Thanks,

Jim R.