"Now if you were looking to add water volume that's another story, but then you wouldn't be considering a 10"
Just looking to decrease nitrates, so that I can have more corals LOL. Wouldn't a 10 gallon full of macro algae work for that purpose? I really would prefer to have it under the stand, rather than hanging on the back of the tank. I am thinking an overflow box, a tube running down into a 10 gallon that has a deep sand bed, maybe some live rock rubble, and some algae, and a return pump to return it back to the main aquarium. I don't even think that I would need any baffles would I. I could also put my heater in there.
Another option, I found a 100 gallon acrylic with stand, sump, lights and live rock/sand for $300. That tank is 5' long, and 18" wide, I could do anything with that bad boy.