Visitherm Steath heater. Accurate, dependable, submersable, & most importantly with turtles unbreakable.
Turtles r messy, different filters do different things better. Power filters excell at mechanical filtration, when I was running power filters I ran Aqua Clears. I torture tested these filters in my breeding setup, extended intakes, packed them with floss for mechanical filtration, & never burnt them out.
For bio filtration, canister filters r the best thing short of a sump, & Eheim makes the best canisters. Many aquarists have these running for 20+ years, they r German engineering applied to aquatics. Eheim makes the pumps for the space shuttle, just to give u an idea of how highly regarded this company is.
Visitherm Stealth heater, Aqua clear & Eheim filter, & ur turtle tank will run better than u could ever imagine. This is the setup I use for freestanding tanks with messy fish, such as oscars & common plecs.