Iphone Pool Chemical App.

[robquick]

Hi,

I've downloaded a app for my iPhone that helps you calculate the quantity of chemicals needed to manage your tub/pool. The design and layout of the app is fantastic and it caters for FC, CC, ALK, PH, CAL, CYA and SI. Having played around with the app and reviewed the numbers it comes up with I have one question about management of Combined Chlorine.

When calculating how much Chlorine is needed to 'shock' a tub that is experiencing high levels of CC what needs to be taken into account. Is it the current level of CC or CYA that dictates the required quantity of Chlorine needed to bring CC back in line ?

Thanks.

[chem geek]

You can validate that the app you are using is reasonable by comparing against http://thepoolcalculator.com'>The Pool Calculator. As for Combined Chlorine (CC), you should not measure that too soon after your soak since chlorine will combine with the chemicals from your sweat and urine to form CC and chlorine will continue to oxidize it (assuming you add enough chlorine after your soak) so the CC will drop. If you are dosing properly, the CC should mostly drop in 8-12 hours and 24 hours later just before your next soak (if you soak every day) and that's when you should be measuring it. You should also use an accurate FAS-DPD chlorine test kit as you can accurately measure CC to within 0.2 ppm (when using a 25 ml sample size).

As for getting rid of CC, the 10x rule most often quoted by the pool and spa industry is wrong. It doesn't take that much chlorine to get rid of the most common types of CC. It takes less than 1x for monochloramine and less than 3x for chlorourea. Using a higher chlorine level just makes the process go faster. And yes, a higher CYA level will lower the active chlorine level which is roughly proportional to the FC/CYA ratio.

[robquick]

Chem Geek,

If the CC figure submitted is above the target of 0.5 it says that the tub needs shocking. However, if the CC level is 1 or as high as 10 the amount of chlorine is says to add is the same figure. If I change the CYA then the chlorine required changes massively.

I assumed the higher the CC the more Chlorine would be needed to shock. On this app it appears that once the CC is high enough to trigger a shock its only the CYA that impacts the amount of Chlorine thats needed. Does that sound right ?

I don't see a CC calculation on the program you mentioned ?

Thanks.

[TdiDave]

What app you find? I wouldn't mind trying it out.

[chem geek]

The Pool Calculator doesn't have a CC calculation. I meant that you could use it to verify the other water balance calculations.

Yes, it sounds like the app you are using has a CC threshold above which it recommends shocking and then the amount to shock is based proportionately on the CYA level since that would give the same active chlorine level. So it's assuming you want to get rid of the CC at a constant rate (based on the FC/CYA ratio) so the amount of chlorine is rate-based, not the amount needed to get rid of CC. In most cases, you would have chlorine leftover and may need to reduce it, especially in a spa that isn't uncovered and exposed to sunlight.

If your spa is outdoors and exposed to sunlight if the cover is removed, then I would recommend doing that when you shock. The UV in sunlight will help break down some CC, partly through direct action and partly through creation of hydroxyl radicals from breakdown of chlorine.

[robquick]

Chem Geek,

Apologies but your explanation is a little over my head ! Are you saying that the app calculates the required quantity of Chlorine correctly to get rid of CC ?

Thanks.

[chem geek]

Sort of. There's not a magic formula to get rid of CC. If you are using the proper amount of chlorine after each soak, then you normally don't get high CC by the time you next soak. So yes, just shock with what the app is telling you and see what happens to the CC. Or just shock to 10 ppm FC or so and not worry about what the app tells you. When you say "massively", if it's telling you to add huge amounts of chlorine, then that should not be necessary. I think whoever wrote the app might be taking data from tables used to calculate the shock level used to get rid of algae in pools at a reasonable rate. Though you could follow that for CC, you probably don't have to and as I wrote having high CC is unusual (except in the hours after a soak).

[robquick]

Thanks. If I'm honest I'm starting to question my photometer. I've now taken it back to the shop and they are ordering some 'references' to check the accuracy of the kit.

I just can't think of another reason why my CC is so high and secondly why I'm unable to bring it back in line (water is crystal clear albeit I THINK there is a stronger smell of Chlorine than normal).

[robquick]

TdiDave,

Sorry for the delay, the app is called 'Pool monitor'. I'm really impressed with it so far.

Rob.

[njmurvin]

This app looks interesting. Would it work with a bromine spa?

[robquick]

Definitely a question for Chem Geek ! There is no specific place within the app to add information for Bromine.

[chem geek]

You just multiply the chlorine FC amount by 2.25 and that gives you the total bromine amount. The amounts from the app would still be accurate for oxidizers used to create that amount of bromine. The app probably won't work for calculating sodium bromide for creating a bromide bank nor for brominating concentrate depending on what is in it (though usually they are mostly Dichlor so you could just pretend it's all Dichlor).