calling all pool boffins!

[tree-peony]

righty, first off, I do know a bit about potable water treatment, but am clueless about pools!

we're having a problem with our pool in Gozo, and our lovely pool man is at a bit of a loss. He doses with chlorine and within 24 hours the entire lot has gone. I've checked this myself. Yesterday he dosed early morning and I checked the level personally mid afternoon and it was showing 3ppm with DPD no1 (which from memory is free chlorine??)

this afternoon, zippo, zilch nada (ie less than .1)

pH is running at about 7.8 so OK I think. No sign of slimeyness. Pool gets full sun for about 10 hours and current water temp is 29 degrees.

Has he got a dodgy batch of chlorine? Suggestions, comments etc more than welcome. What should I be looking for on the packet to make sure it's the right stuff?

[fincafern]

Could be several reasons - I am no expert but my kids work in a pool shop and we have to be very careful with the heat here in Spain with our pool, so I will try to help as best as I can. I am sure here are more qualified to help here, but here goes -
1. High water temp -
When temps go over 26C you need twice as much chlorine for every 5C, so to cure, you would need to keep a close watch and increase the amount of chlorine.
2. When did you last superchlorinate ? If you have a build up of pollutants caused by low chlorine levels you get an increased chlorine demand and will need to superchlorinate or shock.
3.The sun's UV could be decomposing the free chlorine. You would need to add cyanuric acid 500gms to 50 cu mts or you could change to trichlor tabs.
Another cause is too much chlorine which wouldn't give a reading either, but you say you got a reading so it doesn't sound like that.
Hope this helps a bit.

[tree-peony]

hmmm it can't be organic matter complexing with the chlorine as the pool was originally filled with mains water and he's had the problem from the start.

I'm beginning to think it really is the chlorine as apparently he's having the same problem with the other pool he looks after.

[la vache!]

I agree with everything that Fincfern says! When it is hot, the chlorine does disappear more quickly and I have to do shock treatment every 2 weeks minimum. The quality of chlorine can vary - the stuff I can get in supermarkets is cheaper, but not nearly as good as the chlorine tablets I get from the pool supplier.

[cc]

I buy the slow release chlorine tablets, the others disappear too quickly.

[tree-peony]

thanks for all your advice...I'll pass it on

[Bellywobble]

Is everything else OK? I think sometimes if the PH is out you can get a false chlorine reading. Could be wrong though.

[tree-peony]

pH is a weeny bit high, but nothing shocking, and the water here is very hard

[Jimbo]

My chlorine level skittles down very quickly during hot weather, needing careful checking and regular shocking to maintain appropriate concentrations. Interested in LV's comment that supermarket chlorine isn't as good as the pool shop stuff. I've always used supermarket chlorine but could be persuaded otherwise. Anybody else noticed this?

Jim

[Richard D]

It's worth checking the "ingredients" listing on the side of the tub. I remember comparing the cheapo home label with some much more exensive brand in the pool shop once and the actual chlorine content was much the same so I went with the cheaper brand and it worked fine.

Does your tub have details about the ingredients ? If so it could be worth reporting them here and we'll check against what we're all using !

[The Olive Grove]

pH is a weeny bit high, but nothing shocking, and the water here is very hard

We had a similar problem. Can you check the "total alkalinity", as that is what we discovered was causing our problems.

We also have very hard water and it took 37 litres of concentrated liquid acid to get the total alkalinity corrrect. After that everything else fell into place.

I am not any sort of expert, but this worked for us.

[tree-peony]

ah yes, now THAT is a very valid observation

[Jimbo]

Does your tub have details about the ingredients ? If so it could be worth reporting them here and we'll check against what we're all using !

Seems like a good idea Richard, thank you.

Thought mine would have a long list of ingredidents like a supermarket ready meal but it only says:
Clore Lent: L'Acide Tricholoroisocyanurique 980g/kg
23 Euros/5 kilos from local Brico.

Wot, no shark repellent?

Jim