Would a 40 gallon tank be big enough for a 4″ and a 5″ musk turtle (stinkpot)?
The rule of thumb is 10 gallons per inch of shell (cumulative), which would mean a 90-gallon tank for those two. However, area seems to be more important than volume, so you might get away with using a 40-gallon breeder tank or (better) a 4′ stiff-sided wading pool. The smell will depend on how big the filter is, relative to the volume of water; how often and thoroughly you clean the tank; whether you feed the turtles in the tank or in another container; and how much junk you have in the tank. The filter does make noise but it is white noise and fairly soothing. You will stop noticing it very quickly.
