Diana -- I will scrap the shrimp idea then. I did think about painting the underside of the hood white, but then i thought that the aluminum foil would be better. I will paint it white. It can be done cheaply, will last longer and wont electrocute me
"Run the up-tubes to the back corners under the plant substrate, then up." I didnt understand this part. Could explain this to me a bit more please. Also, i dont know what up-tubes are.
-- I read somewhere that undergravel filters are good because they help in breaking down the harmful chemicals in the water because they feed the bacteria in the gravel/substrate. If sponge filters would do a good job with a full plant substrate bottom, i wouldnt mind spending some cash on that.
I think (I can't say for certain) that what Diana is referring to is to effectively reduce the UGF to just the front part of the tank. Most of the typical UGFs I have seen are basically plates that sit ~1/2"-1" above the bottom of the tank, and in the back corners, have round fittings that a (typically clear) tube fits into, and this tube has an opening near the top. Then airline w/ airstones are put down the tube. The bubbles are contained with in the tube, and as they float upwards, they carry some of the water with them, creating a current. The water flowing up the tube with the bubbles comes from underneat the UGF plate, which in turn is replaced by water circulating through the gravel.
If you have a modular UGF (a bunch of squares/rectangles that snap together, or similar), you could just do one row in the front, and then rig up the tubes with an elbow so the go towards the back of the tank along the bottom, and then up the corners. If it's a single piece, you could try laying a piece of plastic over the back part (blocking all the holes so sediment doesn't fall in, and then putting your plant substrate on top of that, and just using the front part for filtration.
Anyways, I think sometimes people over-complicate the idea of biological filtration. Basically all you need is something with surface area for bacteria to grow on (gravel in a UGF, sponge in a sponge filter, Lava rock/pot scrubbers in a wet dry, etc.) that has oxygenated water flowing through it.
While you can't entirely neglect filtration, having your tank well stocked with growing plants will reduce the need for it, since the plants will directly take up a lot of the compounds the filter would be breaking down (ammonia, nitrate, some maybe some nitrites).
And as to the lights, I've coated the inside of a hood before with aluminum tape (I think it's used for ductwork, it's slightly heaver then aluminum foil, and adhesive), but a good white paint will probably be better since the effectiveness of something like aluminum/mylar as a reflector is very dependent on the shape, where as white tends to scatter the light more, so is probably a better option for most hoods.