Alright. So the 45gal long that I had isn't going to work because the seams are too far gone and it's leaking from pretty much every seam it has (thankfully I found this out while it was outside, not after I'd gotten it in the house and set up!). However, a friend of my parents' has a 55gal (or a 50gL...the lady wasn't entirely sure) that she doesn't need anymore, so she's going to give it to me for free. 
However, this presents somewhat of a quandry for me. The 45gL was perfect because it was 18" deep, and after adding a 2" sand bed, it would have been 16" deep, which is right at the upper safe range for bettas (this is going to be a betta sorority/community). A 50gL is 20" deep and a 55gal is 22" deep, both of which are too deep for bettas, regardless of having a 2" sand bed. I'm really thinking this is a 55gal because they're more commonly seen than the 50gLs. Anyway, I need a way to decrease the depth of the water without lowering the water table and still keeping sand as my main substrate. Is this possible? My only idea I've had is to get pea gravel (like I had in the 46gal...it's larger diameter at about 3/4" and cheaper than aquarium gravel, which is a plus) and put it 2" deep, then layer my 2" of sand on top of that. Yes, some sand will sift through the gravel, but it shouldn't be *too* much. I've been told that a 4" sand bed is too deep to avoid gas pockets unless I want a "horde of MTS" routing those out for me (thanks, but no).
However, this presents somewhat of a quandry for me. The 45gL was perfect because it was 18" deep, and after adding a 2" sand bed, it would have been 16" deep, which is right at the upper safe range for bettas (this is going to be a betta sorority/community). A 50gL is 20" deep and a 55gal is 22" deep, both of which are too deep for bettas, regardless of having a 2" sand bed. I'm really thinking this is a 55gal because they're more commonly seen than the 50gLs. Anyway, I need a way to decrease the depth of the water without lowering the water table and still keeping sand as my main substrate. Is this possible? My only idea I've had is to get pea gravel (like I had in the 46gal...it's larger diameter at about 3/4" and cheaper than aquarium gravel, which is a plus) and put it 2" deep, then layer my 2" of sand on top of that. Yes, some sand will sift through the gravel, but it shouldn't be *too* much. I've been told that a 4" sand bed is too deep to avoid gas pockets unless I want a "horde of MTS" routing those out for me (thanks, but no).