Well, they arent 'bent', but the mfg does do something with the facing... I cant remember what exactly... to make sure that the panels bow inwards if anything (and then hopefully the water pressure evens this out).
I suppose, a circular version would eliminate this concern... or perhaps a hex or oct design... shorter sides will show less bowing... to the point where it may not even be a concern. I could see bending a large circle actually being a cost effective way to do this. For a 12" tall 0-edge, you would be able to get away with 1/2" acrylic.. I mean... whats it going to do? Bow out? Lol. If you made the circle wide enough (like a 3' diameter) distortion would be minimal as well.
As for the check-valves... I dont care what it is... if its rated 5-6 years on a pool, it will last 1 year on a reef. Pools dont have biofilms and critters that build up in the piping... they are 'sterile'. All you need is a tube-worm (very likely too) to deposit itself on the valve and your valve will fail. Monthly cleaning would be a possible solution... but who will do that?
My suggestion would be to run the return through a standpipe in the center that runs to the top of the tank. You could have a hole at the top, or the entire outlet, and this would prevent back flow. To cover this up, you could then use aragacrete or some drilled live rock to surround the pipe and make it blend in. It would require a pillar somewhere in the tank though... which you may not want.
If you have the ability to plumb behind a wall or something, there is another, better option as well...
You plumb the pump output up into a PVC standpipe... 3" or 4" diameter with a capped bottom and open top. Then this pipe provides the static pressure for the discharge into the tank. The diameter of this pipe isnt so important, but its height will be determined by the flow of the return pump, and the diameter of the pipe from the PVC standpipe to the bottom of the tank... a smaller diameter pipe, or higher flow pump will require a taller standpipe. Since these style tanks often rely on the sump return pumps for all of their flow, this could require a very tall standpipe or very large inlet pipe into the tank... not that its that bad.
I suppose, if you wanted, you could make the standpipe shorter, and use one of those float-valves like Beckett skimmer collection cups use.... when the water level in the standpipe is full, the valve would close, and when the pump shuts off, the ball would drop/open and the standpipe would have its top open. Still... its a valve that can fail, but in a much more reliable manner.
Either way, this would allow for not needing a standpipe in the tank, or a check-valve. It would mean running a couple pipes through a wall, or perhaps just having a box standing next to the tank (perhaps you could even disguise these pipes into the light hanging system by putting the feed hose in through the bottom of the standpipe next to the tank, so all you would see is a 2-3" diameter pipe, which could also hold your pendant lighting).
I also have shown how to do the drain plumbing. A primary drain with a valve on the output will allow for silent operation (until the valve clogs, and then you would hear that you need to adjust the valve/clean it). The secondary is the backup when the water flow through the primary varies... but the small amounf of water running through the secondary keeps the noise and air to a minimum (on my tank, you cant even tell). This also comes in handy for a skimmer... if you use a recirculating skimmer, you can plumb the primary line right into the skimmer (make sure the skimmer uses a telescoping standpipe, not a gate valve on its output).
I think escape attempts are just part of owning one that you have to deal with.
