Hi everybody! I just had to add my experience to this truly epic thread!
I started the hobby with a 46-gallon FOWLR tank with HOB filter, HOB CPR Backpack skimmer, and a tiny HOB refugium. It never really performed the way I wanted. This was probably because it was too small and I was too inexperienced. I finally decided to upgrade to a bigger tank.
I planned to build a 75 gallon tank, stand, and 20 gallon sump with a C2C internal Beananimal overflow box back in March 2014. And of course I had to do everything myself. Yes, I read nearly all of the posts in this thread until I felt I understood the design, the reasons behind it, and the pitfalls to avoid. I built the frame for the stand and took it to my Dad's to use his table saw and workshop. We built the entire stand over the weekend and I took it home to finish. It took months to figure out how the plumbing was going to go before I could finish the stand.
I bought a 75 gallon glass tank from PetSmart and a 20 gallon long glass tank from Petco. I bought diamond hole saws, plumbing parts, a Reef Octopus protein skimmer, a Mag 9.5 return pump, bulkheads, silicone caulk, woodworking tools, stain, polyurethane, PVP pipe, more from Amazon, Savko, Home Depot, Ace Hardware, and more. I learned plumbing techniques, and learned the hard way that dry-fitting PVC is not as helpful as it seems because nothing fits the same after you glue it. I beveled and chamfered all of the pipe and fittings. I bought custom cut 1/4" glass panels from a local glass shop and assembled them into baffles in the sump and the overflow box on the display aquarium.
Finally, after 4 months of worrying, nail biting, knuckle scraping, re-staining the doors 3 times because they just didn't turn out right, melting the PVC out of the bulkheads with a blowtorch because I put the gasket on the outside instead of the inside of the tank after I had already glued everything together, it was done. It was a miracle I managed to fit all of the plumbing into the sump along with the skimmer; everything barely fits with no room to spare. The plumbing has unions in key locations so it can all be disassembled, and so the sump can be removed.
And it works great! And it's nearly silent! The only noise is the slight thrum of the return pump and the skimmer, but that is kept to a minimum with the doors closed. I have 2 return lines on each side of the tank and each is split into two loc-lines. One loc-line on each side sticks half above the water line to prevent a siphon if the return pump goes offline, so they make a slight trickling noise.
Yes, I had to make a few minor tweaks...
I originally didn't install strainers on the drain pipes in the overflow box because the strainers I had were too long. I learned my lesson after a big snail got sucked in and nearly blocked the opening of the siphon pipe, resulting in a loud sucking noise at 3am in the morning, 3 times in as many weeks. I finally just cut the strainers down to fit; no more snail problem.
I didn't have enough room in the sump for plumbing to remove the clean water from the protein skimmer. It just dumped the water back into the same area it was pulling water from. Clearly it wasn't the most efficient that way and the water flow in the sump just went straight across the top of the refugium section on its way to the return pump. I planted a small ball of cheato but it just faded away, possibly because it wasn't getting any circulation. I finally managed to squeeze a pair of 90 degree elbows to direct the skimmer outflow over the baffles and into the refugium. In addition to making the skimmer more efficient, it circulates the water in the refugium vertically instead of stagnating in the bottom with current flowing over the top.
Ultimately I would like to graduate to the next level and upgrade to a reef tank. I know I need better lighting. I know I'll have to be more diligent about water changes and parameter testing. But at least I have a great system and enough capacity for stability.