How to add chlorine tablets

[dorval]

Hi,
I took my pool water (24' round above-ground) to get tested at Leslie's. They told me that I needed to add chlorine tablets. Last season I used one of those plastic chlorine tablet dispensers where you drop in the tablets and the dispenser floats in the water...tablets never seemed to dissolve maybe because I was using the 3" tablets. Now I was told to put the tablets into the skimmer. I started looking it up online and found out that it might not be a good idea to throught the chlorine tablets into the skimmer because it would cause an inbalance of chlorine and it could possibly damage the liner...is there any truth to this??? Please help me out...I am new to all of this and feel confused now about what to do. Thanks.

[chem geek]

It depends on the specific Trichlor tablets you use. Most should not be put into the skimmer unless the pump is always running and even then that is risky in case of a power outage. Trichlor is VERY acidic and high in chlorine so if there is no circulation, there can be a build up of acidity and chlorine and this can damage not only the liner just outside the skimmer, but also the metal in the pump.

There are special Trichlor products, such as BioGuard Smart Sticks that presumably do not dissolve unless there is circulation (i.e. the pump is running) and that are supposed to be safe to put into the skimmer.

If you use Trichlor, however, realize that for every 1 ppm Free Chlorine (FC) you add, you also add 0.6 ppm Cyanuric Acid (CYA) and the CYA level will build up unless your pool water gets diluted through splash-out, backwashing (of a sand filter, for example), rain overflow, etc. Higher CYA levels require higher FC levels to keep away algae unless you use an algaecide (such as PolyQuat 60 on a weekly maintenance basis).

Richard

[mamcwifey]

Hi,
I took my pool water (24' round above-ground) to get tested at Leslie's. They told me that I needed to add chlorine tablets. Last season I used one of those plastic chlorine tablet dispensers where you drop in the tablets and the dispenser floats in the water...tablets never seemed to dissolve maybe because I was using the 3" tablets. Now I was told to put the tablets into the skimmer. I started looking it up online and found out that it might not be a good idea to throught the chlorine tablets into the skimmer because it would cause an inbalance of chlorine and it could possibly damage the liner...is there any truth to this??? Please help me out...I am new to all of this and feel confused now about what to do. Thanks.

I would not recommend putting these tablets into the skimmer. This highly concentrated chlorine will be sucked directly into your pump/filter, and in doing so will eat the insides of your pump/filter much more quickly than if you put them into the dispenser. Maybe you could tie the dispenser near the eyeball, and this might help dissolve the tablets?

[Backglass]

I would not recommend putting these tablets into the skimmer. This highly concentrated chlorine will be sucked directly into your pump/filter, and in doing so will eat the insides of your pump/filter much more quickly than if you put them into the dispenser. Maybe you could tie the dispenser near the eyeball, and this might help dissolve the tablets?

This is true, but only when the pump is off as the concentrated chlorine sits in the lines/pumps. Pucks in the skimmer isn't a problem if the water is flowing.

Of course the best method is to not use them at all due to the CYA addition.

[mamcwifey]

I would not recommend putting these tablets into the skimmer. This highly concentrated chlorine will be sucked directly into your pump/filter, and in doing so will eat the insides of your pump/filter much more quickly than if you put them into the dispenser. Maybe you could tie the dispenser near the eyeball, and this might help dissolve the tablets?

This is true, but only when the pump is off as the concentrated chlorine sits in the lines/pumps. Pucks in the skimmer isn't a problem if the water is flowing.

Of course the best method is to not use them at all due to the CYA addition.

I disagree. You're still pulling the Cl directly into the pump/filter through the skimmer. You're right that when the pump is off the water becomes more chlorinated in the lines, but even when the pump is on, you're sucking it right on through the filter first. The water is more chlorinated than if you use a chlorine dispenser. By putting those tabs into the skimmer, you're putting the expensive stuff in the line of fire.

[Backglass]

I would not recommend putting these tablets into the skimmer. This highly concentrated chlorine will be sucked directly into your pump/filter, and in doing so will eat the insides of your pump/filter much more quickly than if you put them into the dispenser. Maybe you could tie the dispenser near the eyeball, and this might help dissolve the tablets?

This is true, but only when the pump is off as the concentrated chlorine sits in the lines/pumps. Pucks in the skimmer isn't a problem if the water is flowing.

Of course the best method is to not use them at all due to the CYA addition.

I disagree. You're still pulling the Cl directly into the pump/filter through the skimmer. You're right that when the pump is off the water becomes more chlorinated in the lines, but even when the pump is on, you're sucking it right on through the filter first. The water is more chlorinated than if you use a chlorine dispenser. By putting those tabs into the skimmer, you're putting the expensive stuff in the line of fire.

I suppose the concentrations might be slightly higher than a floater, but I would say that IF that floater was near your ladder, it would cause MORE damage your way as there is much less dispersion & flow. Besides we are talking about 40-60 gallons per minute of water on average flowing past a slow-dissolve puck. I will bet that there is no way that a puck in the skimmer (pump on of course) is even getting close to 10+ppm of chlorine as it would during, say a shock. They just don't dissolve that fast.

Chemgeek: Any idea how fast a puck dissolves at say 50gpm and what the concentrations would be?

[chem geek]

Funny you should ask. I did this very same calculation, but I use a 20 GPM assumption since in my pool I have a skimmer and two floor drains so since that's a slower rate, let's use that as more of a worst-case. When I stupidly put in Trichlor pucks into my skimmer years ago (and rusted the thermometer that was in there because I didn't have the pump running 24/7), it took about 2 days to dissolve instead of the more usual 4 days though it dissolves faster earlier on and slower as it gets smaller, but the 2 day number is reasonable to use.

In my case, I have an opaque cover so my daily chlorine usage is low at 1 ppm FC or less, but let's use a more realistic 3 ppm FC for one day and figure that you use whatever number of pucks is needed for your pool volume to get 3 ppm FC per day. Basically, with the pump running 24/7, you are simply adding 3 ppm FC over a 24 hour period. Over 24 hours 20 GPM is 28,800 gallons so even in a pool of that size, this means that the Trichlor dissolving will create water going through the pipes that is 3 ppm FC higher (and don't forget there's CYA in the water so disinfecting chlorine levels are still very low).

So the net effect is that if you are dissolving Trichlor in the skimmer, then it will likely raise the FC level in the pipe, pump, filter, etc. by less than double the bulk value in the pool. Exactly how much depends on the GPM rate vs. the pool size. Higher GPM and smaller pools would mean even less of an FC rise.

Of course, I am assuming reasonable additions of Trichlor to maintain normal pool FC levels. If you are trying to shock and are using lots more Trichlor, then that's a higher chlorine rate, but still on the order of shock level.

As for acidity, the calculations show that the effect is minimal due to the pH buffering of the water. Again, assuming that the pump is always on. If the pump is off, then both chlorine and acid can build up significantly in the area of the skimmer and this is definitely of concern in the skimmer area (as my thermometer rusting would indicate), but may also be a problem downstream from the blast of acidic high chlorine water when the pump turns on (though this blast is brief, but if done repeatedly could potentially be a problem) and maybe some degradation from diffusion (though that's a long pump run for the chlorine/acid to diffuse through -- I never did that calculation).

Richard