You can rent tubes at the Dolphin & BCV...I know for a fact because I stayed at both places this past summer. They also sell noodles for use.
I see that you're staying at AKV..I'm not sure if they them there... when we stayed at SSR this past May, they did not rent tubes there or have a poolside gift shop.
**When we got to BCV this July, we saw that the poolside gift shop there sells 5 different kinds of SuperSoakers...they exact same ones we had at home in our garage!! I'd have brought them if I'd known...I had to buy two there...one for DS9 and one for DH!!