Oddball tiny plywood tank build

[Raptorfish]

Greetings all.
I was once an aspiring monster fish keeper (largish Malawi haps like Champsochromis, Fossochromis), but built only in glass and kept it under 300 gallons.
Apologies if this doesn’t fit in this community. If you could recommend another place that would have tank build experience on the smaller sizes, I am all ears. Thanks for your time.
I miss my big fish!

Right now I need to build a very small tank built into a larger land-based enclosure, and my boss wants it to be plywood construction with just one glass wall, rimless if possible. This is to be a display riparian habitat at a nature center I volunteer at.
I was hoping the experts here might have some insight into my questions, despite this being a very scaled-down build.

The water section need only be 24”x24” with a water depth of 8”. Only 20 gallons. Max size of 36x30x10 (47 gal)
I was planning on epoxy coating the wood, Pond Shield or equivalent.
my questions are:
1. what is the minimum lip width I will need around the glass to seal it to the epoxied wood? Since the depth is so tiny, a large lip/overlap would eat into an already limited viewing height. I often see builds with 4-5” of overlap but am hoping I could get away with much less with such a small water volume and depth….? How close to the bottom of the pool can I put the viewing pane?
2. Would I need to frame around the glass panel with 2x4’s on edge, or can I go with a thinner frame thickness on this size build? The aesthetics of a deeply inset window is getting some pushback from admin. I was an engineer for 25 years but never worked in wood so I am unfamiliar with the strength calcs for this type of assembly. Links to data/calcs would be welcome and I am happy to do the math myself if no one knows the answer off-hand.
4. Recommended glass thickness if the top of the glass is rimless? I wasn’t thinking starfire or anything, just normal glass. Tempered or no?
5. If the lip needs to be wide or the framing thick, I may just build/buy a glass tank, set it into the wooden enclosure, and camouflage the rim. I assume I can find an epoxy to camouflage the glass walls/floor not used for viewing….but I think I need to have no silicone beads in the seams before applying the coating - is this structurally sound? Add the silicone seam beads back in over the coating? Would some other non-epoxy coating be able to go over the silicone beads instead?

Other thoughts welcome
apologies if this doesn’t fit in this community. If you could recommend another place that would have tank build experience on the smaller sizes, I am all ears. Thanks for your time.
I miss my big fish!

 

[jjohnwm]

1. An all-glass tank has sides that are constantly being pushed outwards, i.e. pulling the joints apart, and yet the tank is held together by a silicone bead that is the thickness of the glass. The interior bead doesn't hold the tank together; it's there just for extra waterproofing, just in case. So, logically, if that construction works, then the width of the plywood lip around the glass in your build can be very, very narrow, since the water pressure will be pushing the glass to the plywood more tightly rather than trying to pull it apart. I think the smallest plywood tank I have built was about 40 gallons, and had about a one-inch lip around the front edge.

2. You don't need any kind of "frame" around the front glass at all, unless I am mis-understanding your question. The plywood front should be a single sheet of plywood, with the window cut out of the middle; no other reinforcement necessary. Even if you cheap out and make the front panel out of four separate pieces of wood, I have found that all you require is an additional two pieces to double up the actual corner joints. Top and bottom horizontal pieces run full length of tank...left and right vertical pieces fit in between these longer runs...then a pair of verticals cut to the actual height of the tank, applied one at each end so that the joints are covered. I've done this a bunch and it works fine, just looks less attractive. In your case, since you don't want that "inset" look, I would suggest biting the bullet and using a single piece for the front panel with the window cut out. The wood you remove will come in handy for making euro-braces, etc.

edited to add: just noticed you are making this a rimless design at the front. That would push me even further in the direction of using a single panel with a cutout for the front.

3. I've got nothing for question 3, because I don't see one!

4. Recommended glass thickness is shown on a bunch of easily-available charts on the internet. I made the mistake once of suggesting a thickness taken from one of those, and was thoroughly lambasted by the OP, complete with insults, name-calling, etc. Not going there again, except to say that you are talking about a single, small, inexpensive piece of glass. No need to go as thin as you possibly can; overbuild it! Especially since the top is unsupported, and extra-especially since it sounds like this will be water-feature in some kind of terrarium-like display? Stronger is always better! Personally, if I were doing this, I'd go 1/2-inch. Tempered or not, whatever you can get. You won't be drilling this pane of glass, so tempered would work fine and apparently be much stronger to boot.

5. You don't need silicone between the wood panels, in fact wood glue should be a given there. You can't epoxy over silicone either, so no silicone bead before painting the interior with epoxy. I always apply a simply finger-smoothed bead on all interior corners after the epoxy is applied and cured, but it's just a confidence thing, totally unnecessary if the construction was careful, precise and neat.

I'm assuming you will be using 3/4-inch plywood for this? That's all I have experience with, and my tanks are left unfinished on the outside, due to laziness, cheapness and also so that any leaks that might develop will be very easily spotted, and the wood can breathe and dry out easily. Even the few tanks I made that were or became "display" tanks were sheathed on the outside with panelling, fabric or some other decorative layer that didn't seal the wood. I can't help but wonder if a tank such as you are describing, sealed inside and out, might experience rotting if water manages to find its way through some tiny pinhole somewhere and has no way to dry out; this might go unnoticed until it's too late to repair?

Nowadays there are other materials you can use that are likely far more advanced and more water-resistant than wood; might be worth looking into some of them. A couple of guys here on MFK who may be able to point you in the right direction are @wednesday13 , @Backfromthedead and @fishdance

 

[M1A1]

Looks like @jjohnwm covered most of what I was going to say, especially the glass thickness question which always draws lots of opinions. Otherwise:
1. I agree with a 1" lip especially due to the 'rimless' request..
2. ... which I assume means there would NOT be a bit of plywood across the top front of the tank, it would just be glass, right? In that case the front plywood panel is a U shape (left, bottom, right) instead of a full square with a window cutout? I don't see any problems with this to be honest as 8" of water is really not much. I would go with 3/4" plywood.
4. This question. My math says for a 24" by 10" rimless (un-braced top edge of panel) 'window' supported on the three other edges, 1" lip, and normal annealed glass then minimum thickness is 0.19" which rounds up to 0.25" as the next closest standard size. I would absolutely NOT go with that size and would go up to the next closest which is 3/8". Even then, since the piece of glass is so small, an upgrade to 1/2" shouldn't cost more than an extra $10-20. Maybe spring for some nice beveled edges on that side...
5. I wouldn't do the drop-in glass tank route myself, I don't see the point of 'skinning' an all-glass tank with plywood, but understand where you're coming from.

 

[Raptorfish]

Wow I am so thrilled with your detailed responses!
Thank you so much. I am off the to drawing board with new confidence!

 

[fishdance]

I would be buying or building an all glass rimless tank and cosmetically clad the sides and back with whatever wood type / desig/ thickness you desire. This is a much simpler safer (reliable) method for public viewing. This will enable no resess and no border overlap that is the brief provided by your boss. The wood sides could be 3mm thick for example. Probably faster and cheaper this way as well.

I would build the glass tank structurally capable of being filled right up or place a small safety drain height hole if the glass thickness is designed for only 8 inches of water.

 

[Raptorfish]

Thanks all for your thoughtful responses!
I am still deciding whether to build or buy the aquarium portion.
One more question: with a plywood/epoxy build for 8" water depth, is it possible to have two rimless viewing panels 90 degrees apart? Current ask is for a 36" face to have a rimless panel and a 24" face next to it. It feels wrong to do this without reinforcing the corner between them - could this be done with a corner post inside the tank?