| | Re: Reaquascaping 20 gallon high
If you have a good old-fashioned incandescent fixture (or if you can find one at a tag sale for a couple of bucks), you can replace the bulbs with a couple of 20- or 25-watt, 6500K CFL bulbs (the spiral kind the screw into a regular socket). A 2-bulb incandescent fixture with 2x 25W daylight CFLs will put out plenty of light for low- to moderate-light species, and only costs a couple of bucks.
Incidentally, honey gouramies don't get very big at all, and are great fish for planted tanks. A 20g setup is fine for them. The flying fox should definitely go back, though...
Given a choice between gravel and pool sand, I'd go with the pool sand... the finer grains are better for plant roots. Just a personal preference, though.