Slider Tutle

Question
We have had our Turtle, Marcus for 1 year.  He is great.  We allow guppies to swim with him for his hunting pleasure, and feed him pellets daily. (Just a few - sometimes he does not actually eat a guppie for weeks)  He is now about 4 inches accross.  We keep him in 20 gallon tank with about 4 inches of water with basking rocks & a heat lamp.  When will e outgrow this tank?
Why does he become grossly bloated at times?  
Is it safe for him to be let loose in the house to explore?

Answer
Based on the comments, I'm assuming this is a Red-ear slider or Painted turtle.

Loose in the house? Not generally a good idea for pond turtles. Not a big deal, but it is not a real natural habitat for them. I've known a few keepers who rig up pools the turtle can enter or leave at will while it roams, but that can be a pain.

Outgrow the tank? Actually, it did that about 3" ago. The rule of thumb is 10 gallons of water per inch of shell.

You'll be better off with about 40 gallons of water. Most of us use plastic tubs or kiddie pools when you get to this size.

The larger tank offers more exercise and is healthier, assuming decent filtration and water cleanliness.

Bloating? Possibly an infection, complicated by the small water pool, which concentrates wastes and infectious materials.

Try http://www.redearslider.com/index.html for more info.