Literally. I've found that of all the algae scrubber sold and ones made up,a credit card works best. It will remove the toughest algae from acrylic. In fact,as you use the card? You can feel the hard bio load on the acrylic- yet you see nothing other than the gray smear and the green algaes. It's really something as time goes by your acrylic seems to look more and more buffed out. Now,nothing like a real sanding and it takes a few years with credit card but I think of it as a bonus.
It also can remove shallow scratches. Take your time and if you accidently dig into the acrylic with the card and see a white scratch? Chances are if you go back and forth over that scratch it will be removed by the card.
I wont say never scratches...its thin and can bend and things can happen. On glass? No problems ever. Will remove hard water deposits and worst freshwater algae easy.
It also can remove shallow scratches. Take your time and if you accidently dig into the acrylic with the card and see a white scratch? Chances are if you go back and forth over that scratch it will be removed by the card.
I wont say never scratches...its thin and can bend and things can happen. On glass? No problems ever. Will remove hard water deposits and worst freshwater algae easy.