I see a few things here of concern, actually.
Most people who acquire turtles honestly have no idea what they're getting themselves into, and when they buy them from a pet store, they're unlikely to get proper advice there, either.
You spoke of the turtle's enclosure as a bowl, and that's a big red flag. Turtles don't live in fish bowls.
They have very specific needs in captivity, and the equipment needed just to keep them alive and healthy can be expensive.
Don't expect to set up a turtle properly for less than $200.
If, upon hearing this, you know you can't afford it, then it's best to give your turtle up NOW, to someone who can afford proper care, or to a reptile rescue group, etc. Do this before the turtle becomes ill, because without the basic equipment to create a proper environment, it WILL. You have already lost one of them.
Here's what you need:
A tank or tub that is equivalent to 10 gallons of fish tank per inch of turtle shell length. (That means that a 4 inch turtle requires a 40 gallon fish tank, or a tub of equivalent size).
The water should be at least 1 and 1/2 times as deep as the turtle's shell length.
I do recommend a plastic tub instead of a glass fish tank. Turtles are terribly messy animals, and a plastic tub will make it so much easier to change the water and clean and disinfect. Never let your turtle's water become cloudy, and if you smell ammonia when you put your face near it, it's time to change the water! Clean water is crucial for keeping them healthy.
You can use a large canister aquarium filter to help lengthen the time between water changes. It should be very oversized, for the size tank and volume of water that you have.
Next, turtles, like all reptiles, need controlled heat. The water temperature should be kept at about 75F to 80F. A submersible aquarium heater can accomplish this.
Sliders require a dry basking area, where they can get completely out of the water. Over this basking area should be a heat source, so that the temperature at 'turtle level' is 90F. Raise or lower the heat lamp to accomplish this--temperatures too hot can burn the animal, too cool, and the animal will be prone to get sick and won't be able to digest its food properly.
Turtles require UVB lighting. I recommend getting a UVB Mercury Vapor lamp. There's a specific brand made with water resistant front, specifically for turtles, and this will take care of both UVB light and basking lamp. It's more practical than buying fluorescent UVB lights, which must be within 6 inches of the animal to do any good, and must be replaced every 6 months, and then using a separate basking bulb for heat.
Next, diet--turtles need more than just turtle pellets. Sliders are omnivores that eat a variety of live insects, small fish, worms, and greens such as mustard greens, turnip greens, dandelion, etc.
Here is an excellent article on slider care: