Clown loaches need pristine water, and should have a 6' tank. How many gallons is this 4' tank?
Here's a nice article on the subject of oscar tankmates~ http://www.oscarfishlover.com/index....tankmates.html
There are other great articles there like what size tank you should have for an oscar.
What about cycling the tank? You don't plan on setting up the 4' tank and adding tankmates today do you?