I have 3 pictus catfish in a 2.5 gallon tank (well there all 1.5 to 2 inches so i guessed thatd be ok i feed the shrinking shrimp pellets and like the food is everywhere how can i stop this problem.
Because 3 pictus cats need more like 35-40 gallons or larger. Your tank is massively overstocked and there's no way those 3 cats will be happy in that tank. If the food is all over the bottom, you're overfeeding stressed cramped fish that will have little appetite.
Get your fish a proper, cycled, filtered, heated tank and you won't have "dirt" problems provided you keep up on your tank maintenance.