Whitmor Chrome 3 Tier Organizer

I trusted that the cart's 250 lb weight limit was tested. I bought this because I am a school teacher, and I felt it would be a useful tool to have at the start of this school year. This cart did not survive its first task: I planned to use an aquarium in my room this year, but the school's water is awful, so I removed water from the tank until it weighed exactly 150 pounds (100 under the weight limit). I transported the tank approximately 1 foot on the balanced linoleum floor before a wheel snapped like a twig and my several hundred dollar tank shattered. I am pretty zen about this kind of thing, so I am over it; however, I am unable to find a wheel replacement online, so not only have I lost my tank, but my 40 dollar cart is worthless. If there is any acceptable wheel replacements online, I would appreciate having them; as would anyone else who actually intends to use this item to its capacity. Oh, and the leg has a slight bend, but that is probably from the inch-long fall to the linoleum (also scratched, ruined) and we can presume the force generated was over its load-bearing capacity; I teach English, so I wouldn't know.