I'm trying to find where to put the everyday supplies he uses like chlorine tabs, poles, filters, etc.

When going through the self-employment business expenses, you can use Supplies section, where you can enter your cleaning supplies and amount OR the section called Other Miscellaneous Expenses can be used to enter your supplies.  You will be able to enter your own description and amount.  Simply say "cleaning supplies" and enter total amount for all the supplies (see pic).