When I got the tank I was given 2 tanks, a 15g and a 35g. I just went threw a box of razorblades working on just the inside of that tank. At least 4 different silicone jobs, and between each patching was heavy hard water stains. That is what kept breaking my blades. The 15 was the cleaner of the 2 tanks.
This comming weekend they both are going to the dump.