Chlorine Loss every 2 days

[GrahamL]

Using chlorine tabs in skimmer, ph good also using chlorine stablizer but after 2 days the chlorine has dissapeared. Pool water blue and clear its a mystery - any ideas ?

[chem geek]

First of all, unless your chlorine tabs are specifically designed to be used in the skimmer, such as BioGuard Smart Sticks®. Most Trichlor tabs/pucks should NOT be used in the skimmer because they are highly acidic and will continue to dissolve even when the pump is turned off thereby building up highly acidic water that can damage plaster near the skimmer and possibly migrate to and corrode copper heat exchangers in gas heaters. Standard Trichlor pucks/tabs are generally used either in a floating feeder or in an inline chlorinator.

I presume that you mean that after a couple of days your Free Chlorine (FC) level measures zero, correct? Or are you saying that the pucks fully dissolve in two days. If the latter, it sounds like you are using standard Trichlor pucks in the skimmer and you should not do that -- they dissolve too quickly that way and have the problems with acidity described above.

If the problem is just that you are unable to keep up with the FC demand, then that is most likely due to your pool building up Cyanuric Acid (CYA) from continued use of Trichlor pucks/tabs. Higher levels of CYA make chlorine less effective unless you proportionately increase the FC level and that's hard to do using pucks alone. Once the FC/CYA ratio gets too low, especially below 5%, then algae can grow faster than chlorine is able to kill it. This often first shows up as unusual chlorine demand and then as dull/cloudy water and eventually green.

Get yourself a good test kit, either the Taylor K-2006 you can get at a good online price here or the TF100 test kit from tftestkits(dot)com here with the latter kit having 36% more volume of reagents so is comparably priced "per test".

Once you've measured your CYA level, if it's high then dilute the water to lower it. Another alternative to dealing with high CYA and not having to maintain a higher FC level is to use a supplemental algaecide (PolyQuat 60) or a phosphate remover, but these are extra cost.

Learn more about maintaining your pool by reading up at the Pool School at Trouble Free Pool.

Richard

[Pooltech32]

If I have a pool with high CYA I will go strictly to a shock form of chlorine, liquid or granular, that way your CYA levels will stop increasing until you get it back to normal levels, but you should always shock your pools to avoid getting high CYA.
For example lets say you add 6 pucks per week to your pool, if you were to add 5 liters of liquid per week your puck consumption would probably go down to 3-4 per week, over the course of a summer that can really add up.

Julian