Answer:

It could be several things that cause irritation and it may take a little trial and error to figure out. First, you may have the grandkids shower and wash before entering the pool. There may be some reaction taking place between lotions, perfumes, etc. On their skin and pool water. The pH could be fluctuating and the right pH is key to swimmer comfort. One other idea would be to shock with non-chlorine shock a couple hours before they swim. This will help to oxidize waste without impacting the chlorine level that is already ideal. It is safe to swim about 90 minutes after adding non-chlorine shock (potassium monopersulfate).