would this be another tank seperate from the RES and river slider? The biggest problem when mixing a RES/River slider and pig-nosed softshell (which the fl softshell is) is if the other turtles are bigger, they see the pig-nose as a source of food...so you may see the other turtles snapping at it. Long term it's not a good idea to mix them. I have 2 tank setups that work well for softies. One would be to take a flower pot and cut an archway in the top of the pot...around the brim...then turn it upside down (so he has a hiding place to get into), then put a saucer on the top to hold some rocks to give your softy a place to rest. In natural habitats, they lay close to the surface under a rock or something so they can stick their neck up and breathe easier without having to move as much. Occasionally they'll get up on the bank to bask out in the sunlight, but very rarely. The other method would to get a piece of plastic cut to the inside dimensions of the tank, and take some aquairum sealant and glue it to the inside of the tank, along with another piece pointing upwards so that it will hold the sand. Fill the tank up to give enough water so the entire turtle can be submerged...then place a small rock to give the turtle a place to get out of the water. Note: Do not use anything except aquarium sealant (available at home depot for about $3 vs $10 at a pet store), because it will kill your turtle. I have used both of these, both suggestions were given to me by blisterburg. I prefer the one with the plastic simply for the reason in my smaller tank it gives a little more room for him to swim around, although it negates his hiding space. When I get my bigger 75 gallon tank in the summer i'll probably go to the flower pot one again.
If you have a fully submerged tank, i.e. no shallow or basking area, that will work for your turtle but it will really stress him out. They can breathe through their skin (the "shell), but not as well as they can through their nose. Therefore you may think the turtle is having fun, but in reality it's almost struggling to breathe when it's getting up to the surface. It's your choice. -Chris
And yes, softy's do need the 5.0 UVB light just like your RES does.