If you try to DIY a 55g, be sure you can provide levels of Co2 comparable to your pressurized setup and that those levels stay consistent. If you can't do that, don't try it at all. Inconsistent levels of Co2 with a lighting schedule designed for high, consistent levels is not a good thing to try. Low light is not a 4-letter word, especially for just a few days.
"Insanity: doing [or asking] the same thing over and over again and expecting different results."