rfmgtp02

I currently have a 55 gallon tropical freshwater tank with plenty of hiding places and artificial plants. It has 5 clown loaches, 2 roseline sharks, 1 red tail shark, 1 striped headstander, 1 golden nugget plecostomus L-81 and 2 corydoras cats. Most of the fish hide or stay near the bottom of the tank and I want to have a school that will occupy the mid to upper levels of the tank. My Ph is usually between 6.5 and 7. i was thinking about about possibly adding about a dozen cardinal tetras to help occupy the space and be a "dither fish" for the loaches. What area of the tank do cardinals usually occupy and can you see any possible problems with compatibility? Any suggestions as to what other colorful fish would school in the higher tank areas? I know i am going to have to upgrade to a larger tank in the future so please dont tell me im overstocked. thanks