water balance problems wih SWG

[dahohm]

We have an 18,500 gallon inground vinyl pool with a SWG. This is our first season with a SWG. The water has been testing fine all summer until recently. We are having problems keeping the FC in the recommended range. We have to add chlorine regularly and that is the only way it has come up to 3. Here are the current numbers. Any suggestions as to what to do to keep the FC up most of the time?? The SWG is now running at 80%. The pool gets direct sunlight most of the day.

Thanks!

FC 2
PH 7.8
CC 0.5
CYA 65
CH 290
TA 110

 

[linen]

My two thoughts (I would probably do both):

1. Do an Overnight Chlorine Loss Test to eliminate the possiblity of algae.

2. Up you cya level into the 70-80 range, that should help with loss you are seeing from the sun.

What is your pool volume?
What swg do you have (and size)?
How long are you running?

 

[Butterfly]

If the water is clear, sounds like you could have a nascent algae bloom eating your chlorine. Regardless, you do need to test (OCLT) to determine the presence of organics, as linen mentioned.

My suggestions:

Today, lower pH to 7.2ish, then continue to maintain FC w/bleach/liquid chlorine.

This evening, turn off SWG and use bleach/liquid chlorine to raise to shock level. Perforn OCLT.

Also, don't add any more CYA until you determine that you are done shocking and/or don't need to shock.

 

[dahohm]

We have done the overnight test and it usually comes up by 1 ppm or so. The pool holds 18,500 gallons. So if I lower the PH today and then turn off the SWG and add enough chlorine to get to 3 to 5 ppm or do I need to raise the FC more? We are running the pump 12 hours a day and the SWG at 80 %.

 

[linen]

We have done the overnight test and it usually comes up by 1 ppm or so. The pool holds 18,500 gallons. So if I lower the PH today and then turn off the SWG and add enough chlorine to get to 3 to 5 ppm or do I need to raise the FC more? We are running the pump 12 hours a day and the SWG at 80 %.

The overnight test needs to be done with the swg off. I would raise your FC using bleach/liquid chlorine up towards the FC shock level of 19 ppm (per poolcalculator.com), since this will give you the best OCLT measurement. If your OCLT (again with the swg off) is more than 1 ppm, then you have organics and that is likely one reason why your swg can't keep up. Make sure you read and understand the OCLT process, so that you do it correctly the first time. Let us know if you have questions.

 

[dahohm]

We did the OCLT. Last night it was 20 and this morning it is down to 18 ppm. PH is 7.2 and CC is 0.5. Water looks very clear but we are losing chlorine overnight. Do we need to shock again today or go ahead and turn the SWG back on and see if it can keep up. Thanks!

 

[elwood58]

You need to stay in shocking mode until you no longer have the overnight loss of chlorine. Then, if CC is zero and the water is clear, back to SWG.

 

[linen]

Elwood has given you good advice...continue the shocking process until you meet all three criteria (also in my sig).

 

[dahohm]

Ok thanks for the quick reply. Also, can we swim during the shock process? All the other numbers are fine and the water looks great.

 

[linen]

Hopefully this won't take long, I would do another OCLT tonight.

Also, can we swim during the shock process?

Our recommendation is you can swim up to your FC shock level as long as the pool is clear. Makes sure you give some time between swimming and doing the OCLT tonight, since having swimmers also consumes chlorine.