We just returned back from CTI a few weeks ago and utilized what we call "the Buddha pool" a few times. If you would like to use it during the day they want you to let them (the spa ladies) know. We used it during the day once, but twice in the evening. The evening was nice because they still have the dim lights on for you. During the day the whirlpools at the spa are one for men and one for women. But at night its open for anyone. We sat in the whirlpool one night for quite awhile and it was nice. All 3 times we used the spa no other couples were there. We had it all to ourselves. When I asked the Spa lady about it she said most people think you have to pay for spa services to use the pool and whirlpool, when indeed you do not. The only advise I have is to bring towels for there is none available after the spa closes.
I got sick (nothing to do with the vacation) during my stay which put a damper on my ability of doing much. But even just laying on the beach, pool & whirlpool was enough for me to want to go back.
Enjoy your trip, relax and "welcome home"