Filtration is one issue that cannot ever be ignored when keeping aquatic turtles. They produce a lot of waste material which quickly fouls their living environment. The best way to ensure that their proclivity doesn’t cause health issues is to purchase a filter which is the rated for the next size up from the actual tank size you have. In other words, if you have a 50 gallon tank buy a filter rated for tank size of 75-100 gallons. There are numerous filters designed for use within an aquarium setting but not all of them are a good match for a turtle enclosure. Even some of those “designed” for use with turtles are poor in their abilities to maintain the necessary water quality required by aquatic turtles.
The very best solution when it comes to filtration for aquatic turtle species is the canister filter which has intake andoutput tubes which are placed in the aquarium itself and the canister resides below the actual aquarium itself. These of course are the most expensive as well but they make it easier to create a naturalistic environment as they lend themselves to the creation of waterfalls and other such water features. These also require less maintenance in my experience. For a single turtle enclosure you can do bimonthly cleanings versus the weekly cleaning required by most other filters.