You’re going to drain as much water as possible and then wipe down the entire enclosure with a rag removing any algae and other materials that the filter somehow missed. After that you’re going to add all the water back as well as the turtle and then after the tank is refilled you will add the filter and plug it in. After about ten minutes plug the heater back in the reason for the time lapse is that sudden shocks of temperature drop to the heater may cause it to malfunction. Never for any reason, place your mouth on the siphon to get it started as you may get more than you bargained for with used turtle water.
Dietary needs are met through offering a varied diet of greens, fish, shrimp, worms, and even crickets. In my experience the juvenile turtles will eat just about anything. I prefer feeding frozen foods like krill and live worms such as night crawlers. For greens give a rough chop to Green leaf lettuce, dandelion greens, red leaf lettuce, endive, kale, romaine, and zucchinis. I would make about half cup of this mixture and place that in the aquarium to float around.
You’ll have to remove this daily and I use a fish net to do so as the juveniles will only eat small portions but once you figure out what they will eat its easier to adjust the amounts of foods to their needs. Adult Red Eared Sliders Trachemys scripta elegans diet will be 75% plant matter.