Chlorine conundrum

[joecoyle]

Hi

I've got a bit of a conundrum for you all.

Here are my latest set of test results:

FC: 4
CC: 0
pH: 7.5
TA: 80
CH: 60
CYA: 35-40

I noticed some algae creeping up the sides of the vinyl, so i open Pool Math app and tap the SLAM button. My SLAM level is 16, and the app says add 2.1 litres of 15% bleach.

Duly added (actually closer to 2.5 litres (finished off the bottle)).

Test again 4 hours later and my FC is only at 7.5.

The 'Effects of adding' part of the app says adding that much bleach should have added at least 12 ppm of FC to my pool (volume: 26,500 litres)

Where did all my chlorine go? I highly doubt that it was used up in killing off the small amounts of visible algae... but maybe?

That said, I did buy 20 litres of the 15% bleach off eBay for £20 (and there are no date codes on the bottles) so i guess it could have been sat in a warehouse for 12 months and lost all its strength??

Thanks
Joe

ps. I'm still trying to work out if its better / more cost effective to use 15% bleach or just a normal 5% 'janitor strength' one and just use more of it. (our bleach in the supermarket is 3% and has all kinds of scents and thickeners)

 

[Steve_in_C]

The algae will consume the chlorine. In the beginning of a SLAM, chlorine will be consumed quickly. Read Pool School - SLAM - Shock Level And Maintain

This is what is supposed to happen.

 

[joecoyle]

The algae will consume the chlorine. In the beginning of a SLAM, chlorine will be consumed quickly. Read Pool School - SLAM - Shock Level And Maintain

This is what is supposed to happen.

Hi Steve,

yeah I'm aware of the SLAM process, and know that Chlorine will get consumed quickly.

This could almost have been a pre-emptive SLAM. There was virtually no algae, just the mere beginnings, so i was trying to stop it before it got a hold.
Thats what I found odd, that such a small amount of algae could consume so much so quickly.

Thats why i was wondering if there was another reason for the lack of efficacy of the chlorine.

If adding that much and those results are expected then thats fine. But normally when I SLAM, my entire pool has algae on the bottom or sides for example. Then I can understand the chlorine being consumed quickly.

Thanks
Joe

 

[zea3]

It also could have been stored in the heat before you bought it. The only way to know for sure is to buy fresh bleach, use it to dose the pool and then test again after 15 min. If the pool reacts like you expect the last batch of bleach was probably weak.

 

[domct203]

Algae spores are microscopic. By the time you can see algae with your eyes (green clumps) there are millions of them.

I would surmise that the water had lost its ‘sparkle’ and seemed a bit dull as well.