Well a normal stool that's released should just be a firm solid black-brown-beige color. I have no clue where the pink color is coming from (maybe undigested parts from a frog)? They might of picked up parasites from the frogs or fishes. Try to be careful with those type of diets and rely more on what commonly is sold for them. Most frog hobbyist stick to safe feeding practices in captivity. Try earthworms or roaches if your frogs show no sign of wanting to eat when you place crickets in there. Also, since crickets aren't really quickly moving to provoke a feeding response, try moving them with tongs in front of your frogs or at least getting them to move. An all mealworm diet is not beneficial for your frogs and will lead to many problems down the road.