i can't comment on a good recipe for a 20oz. bottle, but i would like to point out that you will need a considerably larger quantity of mixture to produce enough diy co2 for a 55g. like 4+ gallons more. just a thought...
i guess that needs more explanation. that was just assuming the tank was at medium levels of light. if it's a lowish light tank, you might see a difference in plant growth with a couple of 2 liters.
Not to hijack, but Ive also got a 55, and Im going the 2-liter route with a 20oz bottle for a separator. If one 2-liter produces one bubble, will I need three to produce three bubbles? How many bubbles does a 2-liter make? Does it depend on the recipe used or the type of yeast?
Thanks. Hopefully this info will be useful for OP also.