I've had my 480G acrylic tank for around 18 years now.. Coraline has always been a factor and I'm a bit lazy when it comes to dealing with it. That said, when I'm not feeling lazy, I use a very large mighty magnet with one of their hard algae scrapers/Algae Dozer. These work remarkably well but they do need replacing as the hard sharp edge will wear down. I swear by the Might Magnets. Given that my acrylic is 1.5" thick on the front and rear panels, not many magnet cleaners will work well on my tank. Might Magnets have a wide range of scrubbers that are powerful enough to adhere very well to my tank and provide plenty of scrubbing power for my thick acrylic. They are not all that cheap but you get what you pay for and are worth every penny and then some for the service they provide me!
http://mightymagnets.com/pads.html
If you get one and use it regularly, coraline will not be an issue. If you get lazy like me, it will be one of those things that takes some work and pads catching up on it. For me, I don't mind a bit of it along the bottom edge of the tank so I tend to let it go a while before playing catchup.
In the years that I've had my tank, I've only overhauled it twice. Both times, I had it completely sanded and buffed out back to new condition to eliminate the occasional scratches that accumulate over the years. Having said that, scratches are only visible when the acrylic has some algae growing on it or when you are really looking for them and unlike glass, as noted above, they can be removed with a bit of sanding and or polishing. You can even scratches while the tank is full with some really fine wet sand paper.
The only thing I caution is that when using the coraline scraper pad like the one I use as well as any other cleaning pad, be careful and pay attention to the pad to insure that if you get some coraline between the pad and the acrylic, you pull the magnet off the glass for a moment to allow the wetside magnet to come off the glass so that the coraline falls away from the pad. Same thing applies to sand or crushed coral which can embedd itself in the cleaning pads and leave scratches.
