Thanks for the update. Most of these large DIY tanks stop posting and no one ever knows the outcome.
Hopefully you make it back into the hobby again. I gave up using wood many years ago. My longest lasting wood tank was 9 years and then several torturous years of constant fixes and patches and stress.
For your sized tank, tilt up concrete slab walls work well. Quite easy to self pour the walls in a horizontal cast, stand up, secure the corners and then pour the bottom. Coved corners and bottom drains even embedded wall jets. If you add key slots into the wall cast, the poured bottom locks in so the bottom can't float up and the walls can't bow out. For only 80cm high, 35mm thick walls would do. Add a sacrificial plastic sheet under the bottom slab pour if you want to demolish the tank one day.
High density concrete (42 - 50 Mpa) is already waterproof (first level). Adding Xypex crystalline additive will self seal voids if moisture occurs (level 2) and a paint on membrane layer (level 3) is a good way to add colour and add yet another waterproof layer cheaply.
Some of my concrete tanks are 20+ years old. I've gotten bigger and deeper as the addiction grows. Glass technology continues to improve.
