Interesting. Conservatively estimating one of the long walls as 8' long and 6' high, there will be roughly 5 tons of force exerted outward. The OP used what appears to be SPF lumber which is quite weak and flexes significantly under force. It also has the property of holding screws poorly because of the weak ray structure (i.e., it splits well).
Since fiberglass and epoxy resin don't flex well under pressure, I'm afraid that the failure mode will be less than spectacular - perhaps a rather large leak as the slow filling process nears the top. But there's a small chance of something much more exciting along the lines of "hey y'all, watch this!" - a high pressure separation of the acrylic viewing window from the tank walls and frame as the walls flex under the high pressure.
"Here, hold my beer" indeed. :lolspin: