I just don't get it

[Wandersen]

Hi all,

I have been having trouble keeping my pool balanced all summer (here in Australia). It is a 32000 liter SWG pool.

My readings last night were as follows:

FC - 8.5
CC - 0
CYA - 85
PH -7.3
TA - 60
CH - 350
Salt - 5400
Pool temp - 30 degrees C (86F)

This morning, the FC has dropped to 3, but the CC is still zero.

I have been having this up and down FC chlorine level for months. My gut feel is to SLAM it - but the pool is crystal clear and the CC reading is zero.

Something is not adding up.

All help appreciated.

 

[aussieta]

if you performed the overnight chlorine loss test
Pool School - Perform the Overnight FC Loss Test (OCLT)
then yes you do need to slam your pool
something is consuming your chlorine

 

[JamesW]

Not everything that consumes chlorine creates CCs.

Most algae won't create CCs.

CCs are mostly from bather waste (sweat, urine etc)

 

[Wandersen]

Thanks. My understanding was that there would always be CCs if there is something in the pool. Now I need to SLAM in the middle of summer :-( How long will it take the chlorine to drop from a slam level of 31 to something reasonable to swim in?

 

[Jezza]

You can swim safely up to your SLAM level for your CYA. It does sound like a SLAM is in order with that kind of FC drop.

You can find that with a SWG you can have algae and it does keep it at bay with the regular addition of chlorine.

The sun burns off the CC's pretty quickly in summer.

 

[needsajet]

My shortest SLAM was 2.5 days. The FC drops fast afterwards if you get a bright sunny day. My SLAM shock level was 20 ppm FC for 50 ppm CYA. When I got zero overnight loss, I stopped adding chlorine, and by the following day at noon it was down to 11 ppm FC (fine and hot both days). I swam throughout my SLAM, and nothing noticeable at all.

Using a shock level at the correct level for your CYA has less active chlorine in the water than a commercial pool at 1 ppm and no CYA.

Happy Australia Day

 

[Wandersen]

Thanks all.

 

[Wandersen]

I am aiming for a FC level of 31, which is high (obviously). Is it possible to do the FC test with a 5ml sample so that each drop is 1ppm to save reagent?

 

[needsajet]

Absolutely! And a good plan during the SLAM.

- - - Updated - - -

and to be sure of your 5 ml measuring method, you can measure twice and pour into the CCL tube, to see if the line is at the bottom of the meniscus

 

[Wandersen]

I'm using a speed stir so here is a 5ml line on that tube in any event - thanks though.

 

[needsajet]

Perfect! So where did you get your speed stir? Aussies haven't been having much luck getting one.

 

[Wandersen]

I can't remember to be honest I've had it for a few years. I think it was eBay and I used a freight forwarder in the US (myus.com)

 

[Wandersen]

Passed the OCLT this morning (FC of 28 last night and this morning) and CC of zero.

We are good to go! Thanks everyone for your assistance.

 

[needsajet]

Congratulations! It's terrific to get the SLAM into the past

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