Posted: Mon Apr 20, 2015 12:57 am Re: Malaysian Box turtle in the same tank as a red ear sider
I wouldn't do it. RES are pretty territorial, and will likely exploit the ambo's comparatively poor swimming abilities to attack. They are from completely different habitats, and their optimal water depths and temperatures are different (temperatures, not so much).
If you decide to get the box turtle, I would encourage you to keep it separately from the RES.
If you're still curious about tank sizes, an adult male RES needs at least a 70 gallon tank. An adult female will need at least 110-125 gallons.
I wouldn't suggest anything smaller than a 30 gallon "breeder" (36X18X16) tank for the box turtle. They don't do that well in deep water, so a wider tank is better than a tall one.