I use aspen in some inside pens and a soil sand mix 70/30 in others. I spot clean daily and change when soiled (smells) or I spill water on the aspen (so it does not mold). If you spot cleaning you can change out the aspen and dirt about once every 4 to 6 months. If your pens are large enough and you don't have alot of torts in them, that is. When I use turtle carpet for the new hatchlings I clean it weekly. (This I wash in plain water with a drop or two of bleach but no soap.)
Mine are all in planted vivariums......for the Redfoot, I take out any poop I find and change the water every day and if he eats the plants, I just put new one's in. Every six months I change the whole thing. For the boxies...they usually poop in the water so that get's cleaned every day, and they never eat the plants, but they do mess them up sometimes, so I also add new ones when that happens, and clean out the whole thing every 6 months. I find that the planted vivariums are much easier to keep clean.