Soggoth43,
How much water is really needed in a sump? What is the desired level? Does the volume of water have any bearing on the effectiveness of filtration? I would think the biological (wet/dry) portion, along with some sort of foam filter between the wet/dry and the main sump reservoir are the important things. What I'm thinking is, the sump water level is probably not going to be running anywhere near the top of the sump tank. If it's too deep, then it will flow back into the wet/dry area and it will no longer be wet/dry, but just plain wet.
Also, how much does the water pressure (i.e. level of water in the sump) above the return pump really come into play? If the return pump is sitting in 10" of water, or if it's sitting in 5" of water (due to evaporation, for example), is that really going to have a big impact on the flow of that return pump? I'm thinking the distance from the pump output to the actual aquarium will have the most impact on flow, as that is the greater distance, and it's on the output side of the pump. And it's a fixed distance. Of course, I could be completely overlooking something here, so please correct me if I'm wrong.
Evaporation is a variable factor in this, I know. My tank will be 36x18 (assuming outside dimensions), so one inch of water is about 2.6-2.7 gallons, depending on glass thickness. Not sure how long it takes for that much to evaporate in my house, but I understand that it will drop the level in the sump faster than it would in the aquarium if I were running a closed canister system. An inch drop in the aquarium equates to about a 2 3/4" drop in the sump. Right now, my 20g long (30x12) loses about 1" of water every 2-3 days. That leads me to believe with the larger tank I'm planning, I'll probably lose 2-3" of water in the sump every couple days. Is it normal to have to constantly top off the water in the sump to keep it running? Is this a daily routine? It's another consideration in my decision to go with a sump. I know I could probably plumb in some sort of auto top-off, but I'm not ready to get that complex yet.
I'm also not willing to drill holes in an aquarium at this point, so I would opt for an external overflow box. Coast to Coast overflows... that refers to a built-in style of overflow that spans the entire length of the back wall of the tank, right? And requires drilled bulkheads? It sounds interesting, and I understand the benifits of that design, but again, I don't want to drill right now.
Good tip on rounding the inside edge of the overflow box lip. Makes complete sense. I bet that has other applications in the aquarium, too.
Interesting about the two output lines. I think I'm starting to understand the basis of these silent overflow designs. I'll have to reread them now that you gave a good explanation on how they work. If I purchase an overflow box (as I probably will this first time around), the models with two drain lines are quite pricey. Is the two line design critical in silent operation, or is it possible to run silent with a single return line? Also, do you run the two separate lines all the way to the wet/dry portion of the sump, or do you combine them at some point above that? I suppose rereading some of these articles will answer that question.
Regarding your comment about overflow siphon and water level in the overflow box, I'm struggling a bit to understand this. If the water level in the back box is lower than that in the front box, and if you shut off the pump, wouldn't the water levels want to equalize, dropping the water level in the front box, breaking the siphon? Or are both ends of the U tube the same length, and the part inside the tank is just in deeper water? Having a hard time picturing this one. Regardless, if I purchase an overflow box, it's design should be such that this isn't an issue, right?
Speaking of commercially-made overflow boxes, I'm still wondering which brands are recommended? CPR, Eshoppes, Tom Aquatics, Lifereef? From what I can see: CPR doesn't use a siphon tube, so trapped bubbles could be a problem; Tom Aquatics looks like it has extra "stuff" involved (not sure what I'm seeing in the pictures); Eshopps PF-1000 has two outputs, uses a siphon tube, and won't break the bank (about $72); Lifereef get's high reviews, and uses a siphon tube, but their double drain model is expensive... $200. Right now, Eshoppes looks to be the best value, but if it's junk, I need to know that.
Thanks for the discussion and the ideas!