I have two 20g longs. One has been set up over a year, the other just a month. I was so satisfied with the first setup, I recently set up the second exactly the same.
I have had a 50% success rate from used tanks. You don't know how it was treated before, what it housed, etc. IMO, to save 15$ish, not worth the hassle JIC it leaks, down the road.
I would steer away from T5HO for lighting for a 20g long. Way too much light with out pressurized co2. Both my 20g longs have this fixture...
http://www.bigalsonline.com/Fish_Li...eries-Double-Linear-Strip-Lights.html?tc=fish
This is a T5 fixture Normal Output. (HO stands for high output). Google the difference, makes my eyes glaze over. However, this fixture comes with the bulbs, is a great price, and is plenty lighting for a 20g long.
You don't need pressurized co2 for a tank that you use T5NO. I faithfully dose 20mL of excel daily. I water change days I stick with the 20mL. I also dose PPS daily. I have too many tanks for EI, PPS seems to be doing the job. Like I said, so far I've not had any problems with algae in my smaller tanks, it's the 75g with pressurized I am constantly battling algae, go figure!
I wouldn't use a HOB for a 20g, but that doesn't mean you can't. I use Filstars, 1/2 my tanks have canisters, just easier to stick with one for parts, etc.... but they are pricey. I've heard great things about the sun suns.
Substrate, I would strongly suggest mineralized top soil capped w/something with a high CEC like Flourite. You don't have to bake the top soil in the sun outside. For my smaller tanks I boil the soil, then bake it dry, in the oven. Takes one day, vs weeks the other way. Tom Barr posts a lot about boiling soil. Baking it also is probably is overkill.
If I ever get my daughter to give back my camera, I'll post some pics.
