That's a good-looking tank...but (and you know there had to be a "but")...
An all-glass tank has certain strengths and weaknesses resulting from the materials and methods used in constructing it. A plywood tank has its own set of similar strenghts and problems. By combining the two in one tank, you are forced to accept a tank that combines both sets of potential problems.
Personally, if I am sealing/waterproofing the interior of a wooden tank, I pay extra attention and devote extra time and material thickness to the bottom panel. Plopping those giant and fairly jagged-looking rocks onto a piece of wood with a couple coats of sealant is a complete non-starter for me. That looks like a future leak just waiting to happen.
Assembling this tank as shown in the video would work, but consider what we are seeing. Even with the video being played at high speed, the painfully slow application of the silicone was making me twitch. Putting the whole thing together at that glacial pace practically guarantees that some silicone will be applied to other spots that have already begun to skin over and cure; not the best way to achieve a strong, watertight seal. Removing the excess bead from the interior and then essentially resealing the interior would be required, and is shown being done...but that's a step that one should only need to do far in the future, if and when the tank ever requires a re-seal. Certainly not something I would want to do when building a new tank. Assembling a new all-glass tank requires having all your ducks in a row ahead of time...all tools and materials laid out and handy...a complete plan firmly in mind...and then a quick smooth assembly, done all at once in minimal time.
Looking at it a bit further...using a razor to scrape away the excess silicone from glass is definitely doable, although it's a bit of a PITA. The removal of the cured silicone must be absolutely perfect and complete, otherwise the finishing bead will not adhere properly. But you certainly can't remove the old stuff well enough from that resin-sealed bottom wood using just a razor blade; I doubt that it can be done using any method. If any of the original bead remains on the wood...and it will!...then the finishing bead must be wide enough to completely overlap that old stuff and join the glass to the "virgin" wood beyond the old bead. You end up with a big ugly wide bead....that is really only doing its job along the thin inner edge.
OP, if your tank is built with the four sides standing on top of the bottom panel, I really think the best way to fix it is to carefully cut away and remove the original bottom panel and replace with new glass. This will require that complete internal re-seal as mentioned above, but it will still likely be the easiest an fastest way to do the fix, and will result in the best-looking fix. It might not be the cheapest way, but if you apply any value to your time and effort, it still comes out ahead.
Otherwise...you will be buying and sealing a piece of plywood, sealing/laminating that to the outside bottom of the old tank, and then also getting a sheet of thinner glass or other material to cover the interior of the bottom, which in turn would still require all that work of re-sealing the entire inside...and will then result in a more fragile bottom panel that might suffer future damage.
Please keep us posted; this sounds interesting.
Backfromthedead
is the guy to ask about this project.
