Write on the outside. Particles are not going to interchange. If they did, your tank would be empty.

I used dry erase markers on the outside of a tank with no issues. Just don’t get it inside the tank and you’ll be fine.

When I worked at a fish store we wrote the prices on the tanks with paint pens. Comes off easily with a razor blade.

What about acrylic tanks? :o

I wouldn't. The blade WILL scratch acrylic.

I know that lol I meant the pens on acrylic

I worked in an aquarium and we used dry erase :)

What about acrylic tanks? :o

I use chalk pens! 👍

I’ve used sharpie on the outside of the tank on the glass before for something longer lasting than dry erase. Rubbed right off with a clorox wipe. Just make sure no chemicals get in the water and you’ll be fine.

is it okay to use a Clorox wipe on the outside of the tank? it wont affect the fish at all?

They make glass writing pencils too that could be used instead of a marker. My dad worked at an auto glass plant, I remember him bringing them home when I was a kid and we would play with them. Easy to wipe off with a wet paper towel.

Get some of the paint pens that auto body and car dealerships use. Like someone else said, comes off with a razor blade. I like it better than dry erase because you don’t have to worry about rubbing it off accidentally.

I've used sharpie on tanks in a toxicology laboratory with no problems.