Safest way to remove spot algae from the glass?

I would never use magnetic cleaners again for the exact reason you stated above. Normally I just use my fingernails and if its still doesn't come off, thats when I take out the razor blade.

Credit card. ok probably not your real currently active credit/debit card, I don't think green spot algae is good for the magnetic strip that gives you Munnies when you use the card. But something of similar nature: grocery loyalty card, expired AAA card, whatever. Hard plastic and a towel handy for drips; scrape down in one motion then, holding just as hard, scrape back up. It's the upstroke that takes off most of the gunk. Move one card width to the side and repeat until you run out of tank, algae or both. Moving up and down keeps water from sloshing around so much and also minimizes disturbance to plants if any.

Yes you get your arm all wet. That's what the towel is for. This aversion to getting our hands in water is what lets the magnetic algae remover industrial complex thrive, and as noted above their devices are both useless and Evil. But the card (mine is a Petco "Pet Perks" card which I care nothing about as their store is too far away and I go there maybe once in five years) method is cheap/free, removes that thin film buildup along with the green spot, black beard or any other crud infesting your tank and makes it all nice and sparkly.

I always stick my arm into the tank to clean the glass or move stuff around. Just wash it before and after. It helps of course to have a tile floor!

Maybe some how attach credit card on a stick?
hahaha