There's other foods you can switch to like mealworms, garden worms and beef heart. List is very incomplete, but i'm sure you get the picture. Like Jexnell said, depending on what you feed them, the poop will be different in color and thickness. The same thing happens when i feed my dempseys garden worms, the poop looks rather gross. If the aro droppings is ok, with solid foods like hikari pellets and sticks. No need to worry at all! My fish definitely do better with large pellets than krill or shrimp. When it comes to making a mess of foods in the tank. I feel the same as you, when it's feeding time and debris gets shot all over the tank. It's nerve wrecking, but a powerful filter will clean it up rather quickly though. Also do huge water changes, when it's time.