What KIND of catfish did you stock? Did you get them from a reputable farm? Bullhead and flathead catfish will root in the bottom sediments and really muddy a pond, even 30 Channel catfish, which root around less, could be stirring water if they are really hungry. Wind/wave action on bare banks can cause a lot of erosion and muddy suspension.

As Chris suggested, get a jar of water and let it set undisturbed 4-5 days. If the water clears on it's own, something mechanical is causing the turbidity. If the water does not clear, I'd opt for alum to clear the water as gypsum only helps about half the time or less, but is always a good mineral source even if it doesn't clear the water.