I'm using a Sicce SDC 9.0 pump. Its a POWERHOUSE of a pump. I only run it on 38% power and it moves some serious water.
I personally just glued the plywood together to laminate it, the wood itself will fail before the bond between the glue and wood is actually broken. One reason why plywood is so strong. If you don't have enough clamps or any, screws will work just fine though. Just make sure you can either hide the screws.
Excuse the chapter book, but I'd like to explain why going the plywood route is worth every ounce of extra labor it takes over dimensional lumber.
You understand my building theory correctly and yes, unfortunately, it would require a table saw to cut everything consistently. I understand the concerns of spanning a 49" opening, however, I would NEVER risk that span with dimensional lumber. Especially with today's quality of wood. As a bit of background, I've been involved in the construction world for almost my entire life, including running my own remodeling company. My reasons for not trusting dimensional lumber is the following reasons. Due to the massive lumber shortage during Covid, saw mills have lowered their quality standards overall, allowing more knots, voids, and rotten wood into the mix. Along with the shortage, it meant that the time line from when the tree was cut, to when the boards where put on the shelf has decreased SIGNIFICANTLY. This means that there is a lot more moisture in the wood and that as it sits in your home, it will dry out and change shape. I've been seeing this ALOT lately in new housing builds with bowed walls, cracked drywall, and other issues to boot. I 100% would never put a glass tank with hundreds of pounds of water on top of a stand that is going to change shape after a few months in my house. These reasons are why at this time, I recommend people to stay away from dimensional lumber for stand builds for the time being. Now if you were to purchase the lumber and let it sit for a few months to dry out, then it would be ok. But you'd need to take care to make sure the boards stay straight and don't warp or twist. Another major issue with dimensional lumber is the growth of the trees. New lumber VS old lumber has a major difference, the growth rings are spaced out much further apart. The wood between the growth rings is made of softer wood than the rings themselves, and due to the curvature of the rings, can greatly affect the strength of the boards. For instance, a 2x4 can carry more load with the thicker edge, but that's only partly due to the thickness of the board. It's also attributed to the direction of the growth rings in the board itself due to "grain direction" of the wood. Grain direction is something I'll touch on a bit later as well. A good comparison, a 1x1 or 2x2, will always break a lot easier if you bend it in one direction vs the other. This is due to the growth ring direction. Give it a try sometime.
Aside from the quality issues with todays dimensional lumber, lets discuss the strength properties of dimensional lumber versus plywood. As previously mentioned, growth rings can attribute a lot to the strength of a board, but due to the nature of.. nature. Not all boards are equally as strong as the next. Grain direction of wood also affects in which direction the wood will be stronger. Boards will break easiest with the grain, which is why 2x4's originally were designed to stand on end as studs in the walls and why in standard building code headers need to be 2x6" minimum. The wood is still strong due to the overall dimensions, but overall weaker as opposed to being stood on end. This is also why plywood was made. Its a lot easier to put a foot through an old subfloor board that's a 2x6" as opposed to even the oldest plywood subfloors. This is because plywood was designed to take advantage of the strength of the wood grain, OSB or orientated strand board, is a literal abbreviation for this. Plywood is stronger, because it it comprised of more hardwoods as well as more layers. The more layers, the more the grain direction varies and the more difficult it is to break. This reason is why you see OSB I beams for flooring joists in new construction, or even LSL (laminated strand lumber) when available. It's because its not just fractionally stronger, its a great deal stronger.
All of this culminates to the fact that when you're talking about putting a glass box full of water, which cannot flex or it will break, on top of something that will inherently flex, you need to be as cautious as possible. I'm sure you could build a stand out of 1x1's and make it hold a 200 gallon aquarium. Its not the ability to hold the weight that we are worried about when building an aquarium stand, its the amount of deflection that will be present with that weight on top of the stand. Deflection causes tanks to burst seams and to fail, I've never once heard of an aquarium just falling to the floor because the stand itself failed. Plywood will have the least amount of deflection and allow you to greatly reduce overall width of wood needed. Is it extra work, yeah a bit. Is it going to be stronger and last longer, 100% no questions asked. In fact, I'd argue that a plywood stand is stronger than a steel stand. Of course this depends on the steel used, but at the end of the day, due to cost, square steel tubing is usually pretty thin walled and I'd be willing to be plywood cut and laminated to a similar overall size would hold its own against the steel in a strength and deflection test.
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