(There are some good
DIY links you may have missed in the
CO2 sticky.)
You can get more than two weeks of total output (maybe a month), but those first two weeks will give nice, high output, and switching the mix early keeps output high, and only takes five minutes or so once you get your routine down
As long as you can keep nominal levels above 30ppm, variance in output with
DIY is not so important. With your light, suggest you just keep changing bottles on the staggered schedule you may have read about. I used 2 2L in ~15gal of total water with some surface agitation (sump), and with a fert schedule and similar lighting grew whatever I could fit into my tanks.
FWIW, I would probably start with the same set-up on a 20g.
You should monitor
CO2 levels until, again, you get your routine down, at which point you will find your levels predictable, and then your first indicator of problems will probably be plant health and algae.
One other thing though, will simply taking the
CO2 airline and putting it into the induction tube for my
HOB filter be an adequate way of dispersing the
CO2?
Sure -
fwiw, this is noisy and not totally efficient for me.
IMO, the efficiency of the diffusor is more important than the mix. An alternative to the
HOB is spending 15min and a few bucks on a nice
DIY powered reactor covers your bases and lets you focus on making sure the yeast keeps outputting (via mix changes or exotic mixes).
Check out Piscesgirl and Zezmo's mixes in the archvies if you prefer longer lasting but more complicated yeast mixes.
Really,
DIY CO2 is only a fraction of the time required for a high light tank. Its very easy to meet your targets with such small volume.
HTH