DIY Refugium Question

Hi everyone....this is my first time posting, so please be patient if I have left off any information......

I currently have a 110 gallon saltwater tank with crushed coral substrate, approximately 140-150 pounds of live rock, a HOB protein skimmer, and canister filter (I have an inline UV light that I will be putting in place on the return side of my refugium that I am about to build). I am wanting to build a refugium in order to do away with the canister filter (if anyone thinks I can't use the refugium in place of the canister filer, please explain???). My cabinet doesn’t allow for much room below my tank and I can't locate the refugium anywhere else in the house (small house). The space I am working with is 36" wide, 14.5" deep, and 19" high. Would a 20 gallon refugium be big enough for my tank, or would I need at least a 30 gallon refugium? I have no plans to move my protein skimmer down inside the sump/refugium. I was thinking I could simply get an old aquarium that will fit under the tank that would have 3 chambers. The first chamber would be where the water comes in from the overflow box, the second being the refugium, and the third would be my return going to the DT. Can anyone recommend an good/affordable overflow box and return pump that will work well together?

I think the 20 gal will be sufficient enough for your size tank...I'm not 100% sure, but a 40 gal breeder may fit under there also. Also, welcome to the site, glad to have you aboard. Eshopps make decent overflow boxes, and I believe the "mag pump" brands are made by danner.

Yeah pretty much any container that will fit in there will do. A used tank is a nice inexpensive way to do it. Definitely ditch the canister filter and keep it for running carbon in a pinch. Welcome to the site!

Since I have no plans to put my protein skimmer down below, what sort of flow rate (gph) should I be aiming for in my refugium? Also, I was thinking about buying this inexpensive tank for $32 off Petsmart Top Fin® Glass Aquarium - Fish - Sale - PetSmart Since it is only 13" high, what depeth of sand bed should I be aiming for? I was thinking if I made the refugium approximately 10" tall that I could have a sand bed in the 4-5" range. Is my logic flawed there? Should I try to make the refugium deeper or shallower?

If you want sand in there, then it's best to do a deep sand bed(4-5in). Most people just do cheato and live rock rubble in the refugium. And you'll want a low-medium flow in there.

Please correct me if I am wrong....

If I am doing a 20 gallon tank for the refugium, I would be in the range of 10-12 gallons in the actual refugium portion? You said fairly low flow....so assuming a 10 gallon section, would I be wanting around 100 gph? My biggest question left in my head is what size overflow box should I be looking for and what size return pump should I buy? I will be moving water up approximately 4 feet from the refugium back into the DT. Does anyone know of a chart that someone has generated online with this sort of information?

I forgot one more question....since I won't have my protein skimmer on the refugium, can I forgo putting in a bubble trap on my refugium? I don't see where I would be getting any bubbles in the system.

Here is a drawing of the refugium that I am thinking about building (its not to scale). Does this look right?