Hi all.
I am an employee at a Pinch A Penny store in central Florida. We are trained to never add granular chemicals of any kind directly to the skimmer. Also to never add any acidic or corrosive liquid chemical there either. All chemicals are to be dissolved first.
Blatantly untrue. CYA is what is known as a 'weak acid' chemically. It will not cause any major change in pH. Adding baking soda (TA increaser) will not cause problems either. All other chemicals should be predissolved. Also, many pool stores (don't know if Pinch a Penny does or not since I don't frequent them since I worked for a competetor) recommend putting trichlor tablets in the skimmer. THAT is a recipe for disaster since it's akin to pouring acid into the skimmer. The problem is that it seems that the are simplifying your training since most pool store employees have a limited, if any, understanding of chemistry!
The reasoning is long term damage and the shortening of the life of the pump and filters. I'm sure you have all heard of the long term damage to equipment that high levels of chlorine can cause.
Pump gaskets, seals, and O-rings are all sensitive to high concentrations of acidic and corrosive chemicals. Deterioration of these lead to premature pump leaks which in turn leads to well premature failure.
Yes, I agree if you are referring to the all too common practice of putting trichlor (which is very acidic, unlike CYA) into the skimmer!
Also, adding granular chemicals to the skimmer can clog the pumps impeller and lead to further problems there. That is one of the reasons DE powder (which is very fine) is added slowly to the skimmer and not dumped in all at once.
No, DE powder should NEVER be added directly to the skimmer, unless you want to clog your pipes. It should be mixed into a 'slurry' with water first and then slowly introduced into the skimmer. Anyone who has ever serviced DE filters should know this but then again, most pool store employees have not (and many do not even own pools!)
Go to the web site "PumpED 101" and read the articles on cavitation. They describe and document the damage that imploding air bubbles can do to a pumps impeller. If air bubbles can do that kind of damage, what do you think granular chemicals might do?
You are comparing apples and oranges here.
Having said all that, I have noticed that alot of you are from northern states where your pool season is relatively short and that you close your pools during the winter. Here in central Florida our pool systems run year round so we experience a lot more wear and tear on our systems. That may explain the difference in the recommendations for adding chemicals to a pool. We repair a lot of pumps and filter systems every day and we also do pool resurfacing. Our techs are pretty familiar with the damage these chemicals do on pool surfaces and pumps etc., but again, you may not experience as much wear and tear as we do.