just making 1 bottle every couple weeks was a PITA... I can't imagine keeping up with 4-5 bottles! But, I will say it is a fun little science fair project. Just keep track of how much time you spend on this (which will be a ton), how many headaches you get from it, etc, etc... and then you will start realizing that the $$$ for pressurized is well worth it
It is "possible"... just will be hard to maintain a constant co2 ppm. and guess what, algae loves non-consistant co2 rates!
Make sure to make a good bubble counter that will seperate out the gunk from each bottle out prior to entering the final tube that all are connected to. Easy to do, so just ask how if you don't know already.
What I used to use, and seemed to work great:
2 cups Sugar (granulized)
1 Packet (or 2 tsp) Bakers Yeast
1 tp Molasses (or protein drink)
1/4 - 1/2 tsp Baking Soda
1-1/2 L's of de-chlorinated water (combo of Hot and Cold)
Desolve the 2 cups of Sugar in warm-hot water (de-chlorinated). Either in the 2L bottle, or a separate container (then pour in 2L bottle)
Put in the 1 tp of Molasses
Fill bottle with room temperature or cool de-chlorinated water to ~3-4" from the top.
Put in the Baking soda and Bakers Yeast
Shake briefly with cap on.
allow time for solution to reach room temperature and it is ready.