Remember that sliders are aquatic animals and they will release their solid and liquid waste into the water, which creates a perfect nest for bacteria. There is a variety of tank tops, some with a light built in it. However, the most important factor of a tank top is for it to allow natural rays of full spectrum lighting. If possible, be able to receive direct sunlight. Most aquatic turtle keepers prefer to suspend a full spectrum light over the aquarium.
Tops are good only if the aquarium is set on an area which receives lots of cold drafts and breezes.
The size of your tank will depend on the size of the turtle and the amount of turtles you have. Remember that the bigger the tank is, the better it will be for the turtle. For an adult turtle of 5 inches a 30 gallon tank will be the minimal size recomended. This is very important. Your turtle's health depends on the quality of the water you provide.