I know the pool you mean, it is at the Sports Sun Centre which is beside the Bus Stop in Los Gigantes, and is also beside the Mimosa apts and across the road from the Sombrero and Hibisco 1 apts.
If you are coming from Puerto Santiago side, follow the coastal path via the steps which are just up a bit from the Tamaimo Tropical. This takes you through past the Sunset apts and Crab Islans apts and turn right on to Calle Hibisco, and if you follow this up the hill, you will see the pool and sports centre, tennis courts, etc quite easily on the left. We have never used it but it looks very well laid out, with grass around most of the grounds surrounding the pool area and seems to be pretty popular with families with young children.
Hope this helps
RJ