Chlorine tab question

[chem geek]

Tabs in the skimmer can potentially damage your equipment. It is the equivalent of pouring acid into your skimmer. If you have a cartridge filter they will damage the cartridge! Not too good for a pump or heater either!

You are correct that tabs in the skimmer can corrode equipment due to the high acidity, but it turns out this only happens to a significant extent if you are cycling your pump. If you leave your pump on 24/7, I originally thought this would put too much acid through the system, but a quick calculation showed that it wouldn't since the puck still took more than a day to dissolve.

One 3" puck dissolving in my 16,000 gallon pool with TA of 100 changes the pH by less than 0.1 ([EDIT]this doesn't count the additional 0.1 decrease in pH that occurs when the chlorine gets "used"; the tablet also[END-EDIT] increases FC by about 2.5 and CYA by about 2.1). If the puck were to completely dissolve in the skimmer in the time for one full turnover of water in the pool, say 3-4 hours, then the pH drop in that water stream would be 0.1, but since it takes longer to dissolve than that, the pH decrease [EDIT]in the water from the skimmer[END-EDIT] is actually smaller.

On the other hand, if the pump is not always on, then the puck in the skimmer will dissolve into stagnant water and the pH can drop to very dangerous levels as evidenced by my thermometer that corroded (this all happened when I first started my pool 3 years ago and stupidly used Tri-Chlor tablets). Then, when this very low pH stagnant water is first streamed through the pump when it turns on, this burst could cause corrosion in the equipment [EDIT]and damage to the cartridge filter[END-EDIT].

Now I am not recommending that people put pucks into their skimmer. I think that's too risky to do on general principle, but it does appear that the end result depends on whether the pump is always on or not.

Richard