they're probably running into walls because its either a a small tank, or b a small over stocked tank....you can get a stealth heater if your freaked out about them bashing into the heater, mind you if they did break it it wouldnt shock them because its not being grounded. ive heard of maybe one instance on another huge piranha site in about one year so very rarely this happens. redbellies are generally the most skittish out of the pygo group. i owned a group of caribe, it took them about one week to maul food infront of me, about 3 months to get them to grab shrimp from my hand, best group of pygo's ive ever owned, not scared what so ever