DAluminum
One week ago last Saturday, I tore down my 55 gallon glass tank and set up a 75. Yesterday I had the pleasure of cleaning the nasty 55 ( going to set it up as freshwater tank for my girlfriend ).
The 55 had been set up as a reef tank for over 2 years. The back glass was never cleaned while it was up and runing, and was about as nasty as you can imagine. Here's what I did yesterday.
Lay empty tank on some cardboard sheets on floor to protect it.
Home Depot - 4" Wide Blade Scraper #66452 - AmericanLine made by Personna - find it in the paint department $5.00 bucks.
Safe & Easy Aquarium Cleaner - by Aquarium Pharmaceuticals - Non-Toxix spray cleaner - get this stuff at your LFS $5.00 bucks.
5 gallon bucket of "very hot water - again Home Depot Orange Bucket $3.00-$4.00 bucks.
BRAND NEW sponge - Home Depot $2.00 bucks.
Wipe down the inner glass surface with hot water. Spray on the cleaner and let it soak for 4-5 minutes. Scrape off the crud. It will come off easily - even if it's really built up. Off came the old algae, corralline and calcium haze. Work in sections at a time and get as close the the silicone seals without knicking them.
RINSE the heck out of the tank with fresh water, wipe down with clean sponge, then RINSE it some more ( you should have seen the look on my neighbors faces while I hosed out the tank in the driveway - little cold in Ohio for this sort of task .. but had to be done )
Took about 1-1/2 hours - start to finish.
If it's a small tank, no problem - one person job. If it's your 55 - you'll need some help wrestling the tank around.
Aside from the silicone seals - this tank looks brand new. Glass is crystal clear.
Hope this helps - and I wish you luck.
Brian