Here's the kind of CFLs to look for. The "soft" white bulb is okay only for viewing the tank. Won't do a bit of good for growing plants. What you need to find are the "daylight" or "bright white" CFL bulbs that fall within the 6500K spectrum. Once you find them at places like Walmart, Home Depot, or Costco.. you will find the specs printed on the package.
Here's an example... notice the blue stripe along the left side of this package. Where it says Daylight, it also shows as 6500K spectrum.