I am thinking about adding a small type of turtle to my 10 gallon planted aquarium with a few small guppies. Are there any that would work? I was looking at the Musk turtle!
A hatchling the size of a quarter or so would do ok in a 10 gallon tank, but 10 gallons is really to small for any aquatic turtle as a permanent home. It would outgrow that 10 gallon tank in just a couple months. You should look at something like at least a 40 gallon breeder for even the smaller species for a permanent home.
Jeff is correct. Fresh hatclings of turtles (that is assuming if you have species such as sliders, cooters, painteds, maps, or another type of basking turtle) should have at least a 20 gallon long, since the ten gallon tank cannot be completely filled with water and there are also obstructions such as filters and decorations so in total there is much less than 10 gallons of water. 10 gallons of WATER is what's required, not 10 gallons of tank.
Some species like mud/musk hatchlings can do well in smaller tanks that are very shallow with lots of bottom area, but they are more frail than the hatchlings of basking turtles. Be warned, mud/musk hatchlings are probably the cutest turtles around, but they're also difficult to get well starteed (striped mud turtles have a reputation for this).