radman

I have a Caldera 3 seat spa (1 pump) that I would like to close for the hot summer months here in SW Fla. I periodially drain the spa but I am quite sure there is still residual water still in the lower level piping, etc. This leads to concerns of growth of algae, mold, etc, if I drain the spa during the summer months. Is there any experience out there in this regard? Thanks in advance for information in this regard, radman