Regardless.
Razor blades sold for stripping paint seem to be a choice of many members, unless the tank is acrylic but you aid you didn't want to reseal them so i assume they are glass.
There are many accounts of people using vinegar, however I've used standard tap water.
Soap, oxyclean, and any other chemicals run there risks that you will need to be willing to take...like you said you have 10 so id assume razor and warm water would eat threw the main stuff...and later on down the road you can work on the tanks that still bug you.