DPD No.1. and liquid chlorine

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
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jpadie
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Joined: Thu 03 May, 2018 02:55
My Pool: 12 x 5 rectangular; steps at the shallow side wall.
Magiline in-ground pool - filtration by cartridges.
1.5HP pump.

DPD No.1. and liquid chlorine

Postby jpadie » Thu 03 May, 2018 03:10

Morning all,

first post here, be gentle ...
I didn't cover my pool over the winter and as a result I now have predominantly a stagnant pond the colour and consistency of a tar pit. Nice.

After a week of filtering and shocking, the water remains very turbid and pale blue/green. No clarity to the water. Filters cleaned

It's had a 20L dose of 10% liquid chlorine on Saturday evening

another two 10L doses on Monday and Tuesday
and a third 10L dose on Wednesday.

The odd thing is that the (cheap) test kit using tablets is reading zero chlorine. Is this a function of the Cl- concentration being so high that any residual colour from the reagent is being bleached out instantaneously? or does perhaps DPD no.1 not react well with sodium hyperchlorite?

thanks
Justin


Denniswiseman
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My Pool: 10k inground fibreglass, Telescopic Cover, Hayward Powerline pump, Quality filter with glass media, 27kw output heat pump, K-2006C test kit
Location: United Kingdom

Re: DPD No.1. and liquid chlorine

Postby Denniswiseman » Thu 03 May, 2018 04:16

Hi Justin and welcome
You really need to get a decent test kit (Taylor K2006C or a TF100) and give a complete list of numbers
FC:
TC:
pH:
TA:
CH:
CYA:
You then need to Slam (Shock Level and Maintain)with relation to your Chlorine / CYA Chart and recommended Pool Levels
You are going the right way with liquid chlorine (sodium hypochlorite) but watch out for the date of manufacture as it loses strength over time and all you are introducing is salt water
High chlorine could bleach out other tests so wait untill that is at the recommended slam level before testing the others
jpadie
Pool Newbie
Pool Newbie
Posts: 2
Joined: Thu 03 May, 2018 02:55
My Pool: 12 x 5 rectangular; steps at the shallow side wall.
Magiline in-ground pool - filtration by cartridges.
1.5HP pump.

Re: DPD No.1. and liquid chlorine

Postby jpadie » Thu 03 May, 2018 09:45

Thanks Dennis,

Amazon france doesn't know those pool kit references.

to be honest, the pool's been highly manageable for the last fifteen years. Last year I made an autodoser for it, from an Arduino and peristaltic pump. That worked brilliantly for the season.

this year I've built circuits to measure ORP and pH with auto-dosers for pH adjusters and liquid chlorine. I'm hoping it will be an even more seamless management than last year (I spend long periods away from home).

the pool often takes a while to recover from turbid water. The bottom filter has never worked and there is not enough turbulence in the water to circulate the water sufficiently to keep the turbidity in the skimmed section. So lots of brushing, lots of cartridge cleaning and lots of 24hr filtering until the clarity comes back.

I'm just confused about the pH reading. Leaving aside the pool water completely, I don't quite understand the chemistry that would cause a DPD tablet to read zero chlorine when reacted with 10% NaOCL. It should knock the socks off the reagent.

Any thoughts on that? The liquid chlorine is newly bought, and is in opaque sealed containers. It smells of chlorine and there is evidently a disinfectant effect. I suspect that the dpd tabs themselves may be the culprit. I've tried several different stips of the tabs though.
Denniswiseman
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Posts: 856
Joined: Tue 06 Sep, 2011 05:48
My Pool: 10k inground fibreglass, Telescopic Cover, Hayward Powerline pump, Quality filter with glass media, 27kw output heat pump, K-2006C test kit
Location: United Kingdom

Re: DPD No.1. and liquid chlorine

Postby Denniswiseman » Thu 03 May, 2018 12:55

Hi Justin
I had to get my K2006c from the states because they are not stocked over here either. Teapot is quiet likely to chip in soon, as he has a place in France and he may be able to advise on a different kit
It seems that you have a good idea about what you are doing technically
A chlorine reading using a Taylor brand PH test, the test results are valid up to a FC of 10, above 18 then are invalid and all of the other brands of PH test tend to be worse.
Bearing in mind the quantity of Chlorine that you have introduced, it would definately skew the tests
Teapot
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My Pool: 12 x 24 (45m3) liner pool, Triton TR60 filter with AFM glass media (Activate) and variable speed pump running 0.08HP
Location: UK

Re: DPD No.1. and liquid chlorine

Postby Teapot » Fri 04 May, 2018 08:43

Hi Justin and Dennis, if the chlorine is high it will indeed bleach out DPD, depending on the tablets obviously. Justin if you buy the two little bottle tester (OTO test and phenol red liquid) from a supermarket this will not bleach out. Technically this is measuring total chlorine and not free chlorine but it will give you an indication.
Regarding turbidity, you have cartridge filters from what I read so you can't use flocculation so unfortunately you have to play the waiting game.

The most important test kit you should have is for cyanuric acid (stabiliser) this can be a stand alone test or if you are looking for a reasonable test kit I can supply you in France as that is where most of my pool work is done.

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