800 gallon plywood tank

The general rule of thumb I use is what ever the recommended thickness for glass is, one up from that. For example 28 to 36 inches would usually be 3/4 inch for glass so acrylic would be 1 inch. That's because of the amount of flex acrylic will have compare to glass. Also the fiberglass is used to reduce risk of cracking and add strength to the tank. He add an Epoxy on top of the fiberglass. You could use liquid rubber. I don't have any experience with it myself. But I've seen others on here use it before.

Acrylic is strong as fare as being able to hold up to stress. It can flex farther without braking. And that's the problem, just because it is stronger doesn't mean you can getaway with using thinner. If you try to use 1/2 acrylic where you should have used at least 3/4 inch or "1. Your going to have a bubble window that will eventually fail. Now I don't know how tall his tank is. Or how tall your tank will be. but if you wanted to use 1/2 acrylic make sure your water level isn't higher then 24inches. You can also raise the window up off of the bottom to change the water height in relation to the window. And the other problem your going to run into is that silicone doesn't stick to acrylic as well as it does glass. You should take a look at the plywood build sticky in this section. And there are others also in the tank section.

on his 800 gallon plywood tank build the fiberglass and resin inside and out has alot to do with the strength.

i tried something similar with a 300g and i didn't do the whole out side just the seems but i did fiberglass the whole inside, my tank bows alot.
liquid rubber water proofs well i used it to save my tank build because of the flexing, i plan on using liquid rubber in my next build but i am going to build a external frame.

i don't know how well liquid rubber will hold up with salt i would call the manufacture.

for the acrylic thickness i'm no expert but i think for 3' you need at least 1 to 1.5" i believe just because acrylic bows alot.

for sealing the window in you will need to do a fiber glass bridge between to silicone and liquid rubber or if your using acrylic you can go with a gasket method or i have seen a build on another form where he used the liquid rubber to seal in his acrylic window on a 2200 g build.

Yeah that should be thick enough. According to the site the acrylic sheet will be 33.5 inches tall. With 1 inch you could go up to 36 inches if you wanted to.