I have Acrylic and bare bottom tank. I used to have sand but yanked it after one or two "quick" cleanings cost me with a piece of sand getting under the magnet and causing a deep scratch. The good news is as stated you can buff it out to look like new. You cannot tell it was ever scratched.
You can scratch a glass tank (although a bit harder to do) if you do you can forget about buffing it out.
Plus I like the added security of welded seems vs. silicon... and I don't worry if I accidently drop something that it is going to break my tank bottom.
Acrylic is very clear and easy to take care of with a bare bottom. I have found the plastic blades sold by Kent Marine make cleaning the coraline a snap.
I used to think it was a pain to clean until I found Mighty Magnets! Link below. They have Acrylic safe algae socks and coraline algae dozer pads that fit on your magnets that are a godsend. I no longer worry about going an extra week between cleanings because the harder green algae will start to take hold. The algae pads scrub it right off in one swipe what used to take hours with the Kent scrapers to do.
I used to worry more about the green/brown algae that formed then the coraline. Now I have easy maintenance for both.
http://www.mightymagnets.com/index.htm
I run my regular magnet once a week and stay on the top of the coraline about once a month and then biweekly usually run the dozer to make it all sparkly and shiny...
Razors are not an option... all in all it is 6 to one half dozen to another. It may be nice to have Glass some times and Acrylic others.
