In my area the yellow mustard algae quickly started to attack my pool. I went to several pool stores and about all they could do was sell me shock and test my water. One day I was at one of the home improvement stores and started a conversation with a guy buying some chlorine tabs and he told me to use algaecide worked great got rid of the problem and never had to use shock again. Actually yellow algae is not effected by chlorine so it’s not useful. Now I realize that the pool stores or not there to help me but to sell me.