Sand will just cause a nightmare! I modded one by trimming the impellar (halving the flow) and siliconing in a 3" tall dam to keep the sand away from the motor. It didnt work, I was cleaning noisy annoying sand grains out of the motor weekly. I finally took all the sand out and kept alot of lr rubble in there and it worked awesome as a fuge.
I used one of these as a refugium. I removed the top, added live rock rubble and chaeto algae. Put a small light over it to support chaeto growth and it gives a great place to grow pods.
I did not cut my impeller. If you move the suction tube all the way (slowest flow) and then lift the tube a little and move it a little more the flow will be greatly reduced. If you leave it in the correct location for slow flow it will still be to fast for a refugium.
I have one on my Fluval Osaka 40 gallon and it works great. I added a couple of pieces of lexan to make a bubble trap and filled the main part with lr rubble and live sand plus a bunch of macro. I put a coralife mini PC daylight on top on a timer for 12hrs on and 12 off, stocked it with pods and also run carbon foam in the bubble trap plus phosphate removal media. My mandarin is fat and happy and so is the rest of the tank.
using it as a HOB overflow might work well, even for others, if you simply cut the back part out and added one or two bulkheads, it simply wouldn't flow over and back into the tank, and if the bulkhead gets clogged, it wont overflow, it will jsut cascade back into tank. Plus you dont have to worry abouit a siphon, simply cover the bulkhead up and fill the tank with water and turn the pump on.
sounds like it would work to me, might use that idea for a smaller tank build.
for the time being, I put about 4 lbs of live rock rubble in the aquaclear, and hooked up its intake tube to a tom's surface skimmer. also i jammed some chaeto in there, since it does get a good bit of light from my PC fixture I modded (bent the reflectors a little, really technical stuff).
I run mine with polyfilters and purigen its upflow like a media reactor moves water across the surface of the tank is really easy to change out once the polyfilter and purigen change color w organics so just use it as is , you won"t find a better hang on the tank filter I have three on var ious Tanks , that and Eheim for canisters are the way to go!