they are cool, when they first did that i was scared, i thought they were sick so i called the guy i got them from and he said thats normal. i also learned that they get a new stinger every 4 months or so and the old one falls off (if you dont cut it off) and its still venemous, so i have to learn to watch for that. im scared of them stinging me, but im just really careful with them, ill only touch them if their at the top of the tank and i wont go near their tail or make it seem like im trapping them in a corner. their really small right now, not even as big as my hand. they arent supposed to get too much bigger but either way were getting a 210 gallon tank for them soon. i have to keep them and my pleco seperated because the female stingray (wizzer) bit him and left a mark.. supposidly its a love bite, but i dont want him to get hurt.