Well, i am referring to the cubes that are about 1/2" big in all directions, not flats. I do reuse the thawed food for awhile, should i not?
If you are referring to the small cubes and they are lasting you a month each, then yikes, your fish probably are starving! I have 2 fish in my tank and feed about 1/3 of a cube every other day (I also have 2 cleaner shrimp, a crab, a large feather duster, and several coral as well, otherwise would feed probably closer to a 1/4 cube every other day). The cubes I use are about 1/2" size cubes also. You can take a knife and cut a little piece of the frozen cube off and then dissolve it in a little dish of tank water, then suck up the liquid with a turkey baster (under $5 at any grocery store if you don't have one) and release the liquid into the tank. You don't need to thaw a whole cube to use a part of it. Also, I do believe frozen food can go bad after a few months - not sure how long you've had yours but you might want to pick up some fresh stuff if possible (maybe someone else can chime in on this).
As for lights, my understanding is that as light bulbs age, the wavelengths they emit shift. So a lightbulb that put off 10000k when it was new might begin putting off more red wavelengths as it ages, contributing to algae growth (plants grow better around 5000k I believe). This is one of the reasons that cyano issues can in part be due to old lights. Most lightbulbs need to be replaced about every 6mo, which is why many people have gone to LEDs - although they have a much higher initial cost, they use less energy and you don't have to replace bulbs.
In terms of RO/DI, you can buy an RO/DI unit for around $125 - check out bulk reef supply. If you are buying water from Walmart and doing the normal 10-20% weekly water changes, then you probably easily spend $100 in water in a few months time - why not just make your own instead? It will save you money in the long run.
As far as a clean up crew, you want to try to get a mix of snails - nassarius to help sift your sand, cerith, nerite, turbo snails (these are the really big snails, aim for about 1 for every 10g), astraea. The turbos are particularly good at eating GHA. Just to give you an idea, this is what my GHA looked like when my tank was new before I added turbos; once I added the turbos, it was gone within a few days and it has never come back!
