Filtration is critical — invest in a good filter

Red-eared sliders are messy and a powerful filter is non-negotiable. I learned this the hard way with a cheap filter that couldn't handle the bioload of two adult turtles. Cloudy, smelly water and one mildly ill turtle later, I invested in a proper external canister filter rated for three times the tank volume. The difference was immediate. Good filtration means clear water, happy turtles, and far less maintenance.