Cleaning an old tank

I have a used 40G breeder that was used for fresh water. The dried scum on the glass is tough to get off even with a razor blade.

Is there any secrets to help soften it or is the only answer a lot of elbow grease?

 

i used bleach. Fill the tank up with water and poor about 1/2 gallon of bleach in it, and let it set for awhile. It will come right off there.

 

after you bleach it and clean it put a whole box of bakingsoda in new water in it let it sit for a day a powerhead would help it deactivates the bleach

 

How long of a soak with the bleach water in the tank? Will the bleach start to break down the seal if left in to long?

Thanks for the information.

 

I left mine in overnight and had no issues.

 

You could also try a vinegar mix. That usually works great with my powerheads.