Hello fellow Pinoy! What is your enclosure made of? As far as I know, glass and acrylic can heat up fairly quickly, therefore also heating the water. To entice the turtles to bask, the basking area temperature should be at least 10 degrees higher than the water temp. Natural sunlight is the recommended source of UVB and heat, so there's no need to purchase the lamps, as long as they can get easy access to the rays, and may be able to duck/dive back into the water for a quick dip or drink. The best option is building a pond enclosure. How big is (are) your turtle(s)? oh, and welcome to the forum!