This is a valuable question. I’ve always been frightened off by acrylic tanks. I figured ‘one small grain of sand’ under the scraper, and it’s all over. Scratch city. And yet some of the largest/most expensive tanks in the world are probable acrylic, so there has to be a good answer...
i use an old credit card attached to a scrapper, the plastic is softer than the acrylic so less chance of getting a scratch...i use that for coralline...for film algae i use a modded cleaner in which i replaced the velcro for microfiber cloth, works like a charm
I have used magfloat and flipper in the past but the best one bar far is mighty magnet with their algae scrubber, specially for larger tanks. Best investment I ever made for cleaning the acrylic. It works amazing and worth every penny.
Magic eraser works great as well. Make sure you get the original one without any chemicals.
Depends a lot on the wall thickness. My acrylic tank has 1” sides, so most magnet cleaners aren’t strong enough. I went with mighty magnets. One that will work on thicker walls isn’t cheap, and I’ve no idea if they are the best - only that I have been very pleased with it and have had no reason to regret the purchase.