I am sure that any CO2 added to the tank is better than none. But from my reading, a DIY is not typically enough for a tank of you size, especially with the amount of light that you have.
I never did the DIY CO2 method, so my comments are only based upon reading and research. Due to the size of my tank, I was convinced that pressurized CO2 was the way to go. I am thinking about putting a DIY setup together for my 29G tank.
2) Someone suggested that I have 2 yeast reactors feeding the tank, mostly so I don't have to worry about production drop off (staggard maintenance/refill schedules). Is one PVC reactor enough, or should I think about adding another?
Having the two yeast bottles will allow you to alternate your refill schedule. It should also produce a more stable CO2 flow to your tank. From my brewing experience, CO2 output is on "bell-type curve". During the first stages it takes a while for the yeast reaction to build up. After a while the yeast is churning out alcohol and CO2. Eventually the reaction begins to slow down, as alcohol increases and sugar becomes depleted. By alternating your refills, you can always have one mixture at peak, while you are in the refill/inital stage with your other bottle.
3) If I add a second yeast reactor, can I hook it up to the same power reactor/defussior?
Yes... Get an inline T connector. And anothe check valve (assuming you have one already). Each yeast bottle should go through a check valve and then to the T connector. This not only prevents siphoning of aquarium water, but also keeps the bottles from pressurizing each other during their diffent stages.
4) Do I need to worry about CO2 production at night? It is too impractical to shut off CO2 manually every night.
First, it would be very impractical to try and shut off the CO2 production from a DIY setup.. If you used a valve to shutoff the flow from the bottles, you could end up with quite a mess! For example an exploded bottle from the pressure build up not having a realease. They only impractical
way that you could control the output would be to cool/warm the yeat mixture.
Here is a link to a site that I checked into when I was considering a DIY CO2 setup. It has lots of good info and diagrams which should help: