I recently aquired 2 55 gallon tanks that were left in a apartment when the owner went to jail. These tanks were allowed to evaporate from full to all the way dry. Just filthy. I took them outdoors and hosed them down with lime away and let it sit. Then rinsed and did it again. No scrubbing because the scrubber will pick up the calcium deposits and scrathc the #$%^ out of the tank. Also dont use the steel wool or green scrubbies as these too will scratch the tank badly. If you want it super clean with minimal scrubbing limeaway is the way to go. Just make sure to rinse like crazy when done. Bolth of the 55 gallon tanks that I got free have had fish in them for around 3 weeks and havent seen any problems.