New tank 300 gallon

[abcha0s]

3/4" inch rimless would be over speced.
5/8" rimless would meet acceptable safety standards.

The major consideration is the height at 20"

I prefer over speced, but you will pay significantly more for the 3/4" and if it's not necessary, why bother?

If your interested in how I designed my 300g, you can read my build. If I had a "do over", I would have gone rimless.