High chlorine in pool

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Brekel

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May 19, 2016
13
Hobart, Tasmania, Australia
Hi All.

I've just bought a house with a 7,000L outdoor swim spa (about 1800 gal for you guys across the Pacific)
It was filled up and had been running before we moved in, except that it was shut down for two weeks because the heater element failed and they/we were waiting for a replacement). It runs of a SWG.

The element was replaced the other day, we've brought it up to temp, and I brought a test kit.

The chlorine test (DPD) goes clear as soon as the tablet starts to dissolve (a slight pink during the dissolving) which from what I read previously can be due to high chlorine. The local pool store tested with the same result.

As my wife is keen to get in, I bought some Sodium thiosulphate to bring the levels down and turned off the swg. I've added 300g in stages, which by the calculation on the pack should drop the level by 42ppm. It still bleaches out the test.

If I dilute it down to about 1/5 with tap water, it reads around 5 (max on the test chart).

There are also some pool-check test strips the previous owner left that I believe are a tetramethylbenzidine test. It should go from clear to a dark blue. It goes a dark brown, which I assume means it's still way over.

There's not a lot of sunlight at this time of year and it's pretty cold.

What's the best option?
Leave the cover off throug the day?
Run the blower to aerate it and drive more Cl out?
More sodium thiosulphate?

TIA
 
Hey there :)

Ok, there is a test kit that is exactly like we use here and will help you very much, you have 2 options.. Yes they are expensive there but way worth it...

1. Buy just the FAS-DPD test kit to test up to 50ppm chlorine so your know exactly what you're dealing with. Chlorine FAS-DPD 3-in-1 Kit Clear Choice Labs

2. a complete test kit, this option only if your test kit does not have everything already Total Pool Water Testing Kit, Salt Water Clear Choice Labs

The sun will take the chlorine down but how long is unknown so leaving the cover off will help.. I have never used sodium thiosulphate so I am unsure on its use...

I hope this helps :)
 
You can try Vitamin C (ascorbic acid). We have used this once and it works great. Try it in a sample that you have tinted for the FC test, crush a vitamin c and drop some into the sample to confirm your vitamin C works. My husband crushed 250g of vitamin C in a blender and dropped it in the skimmer. He then tested the water coming out of the return in the pool, there was no chlorine in that water. Unfortunately, I do not have a recipe about how much vitamin C is required. The good thing about this is that vitamin C is fairly cheap and easy to come by.
 
At least I've figured out how the chlorine got so high.
Looking at the way it's configured, when the temp is low the filter pump kicks in, as the heater runs inline with this. The SWG also runs whenever this pump runs - contrary to the manual they left, the SWG doesn't have a timer. So when the heater failed the pump and SWG would have been running continuously due to the low temp. It also would have run continuously while were heating it back up.
The previous owners weren't up with all the technical side, so probably didn't realize.
 
As a follow up on this one, I calculate that my FC must have been over 100!
I took a few measures to bring it down quick, as there was a slight leak in two pumps and I wasn't sure if the high chlorine was damaging the seals or other components.

So I:
- Added the full 400g container of sodium thiosulfate (Should drop FC by 61ppm according to pack, 32 by other calculations)
- Left cover off through daylight hours for a week (should have dropped it a bit)
- Added 1.2 L of 3% H2O2 (should drop 11.5 ppm)
My Clear Choice Labs test kit then arrived, and FC tested as somewhere around 50 still (transition was very slow so hard to be exact)!
Bought a 1L bottle of 595g/L H2O2, did a quick calculation, and added 250 ml in two steps (should drop by about 47 ppm).

Tested a couple of hours later and the pool was at 4 ppm :)

Pump seals now replaced, and all is running well.
 
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