Red Ear and Map Turtles

Question
First let me tell you, we are novices and learning as we go.
We have had map turtles (2) for a year and half and have added two red ear sliders.  Don't know how to tell their gender.  They were all the size of quarters when we got them.  One map turtle is double the size of the other map turtle and the same thing happened with the sliders.  One is twice the other slider's size.  They are in a 20 gallon tank with the UV lamp also a heat lamp over the floating dock that they sun themselves on. We have a filter and a temperature gage.  We feed them in the bathroom sink, so the turtle food doesn't mess up their tank. They appear to get along and it is fun to watch them swim, sun and hide in the(fake)foliage we put into the tank.  Please tell me if we are doing anything wrong so far, so we can correct it.

We noticed that the bigger turtles have really long nails and didn't know if we should try to trim them or not. Should we trim their nails?  We really don't interact with them except to take them out to feed them, because we don't want to stress them out.

Why would one turtle double in size? Our little red eared slider doesn't appear to ever grow.  Yet he/she swims, sun bathes, and hides in the stump provided and appears to be okay.

Any info will be much appreciated.  We are so happy that we've managed to keep them this long and that they are actually growing!

When they get the size of 10 -12 inches, what do you suggest we keep them in?

Answer
Long nails is a male. Some species show this trait as they get older.

Not growing is a sign of stress. I would say that the stress is from being dominated by larger turtles, and being rather crowded.

The rule of thumb is 10 gallons of actual water per inch of shell length. So, I would guess you have a total of about 8-12" worth of turtles, which should be in about 80-120 gallons of water to give each its own space.

You see, turtles in the wild are rarely found near other turtles except for mating and basking- and the basking they do for protection (one sees a predator and slides to the water (which is where they get the name) and all slide in.)

We usually say that a fully loaded 20 gallon tank is right for a single young Slider or Map Turtle, so you may want to rethink the housing.

Good luck, and try http://www.austinsturtlepage.com for some great advice!