Hmm I have a 35gal tank, so the 16oz would last me 6 months?
Is this a good estimate?
At $8 a bottle it doesnt seem expensive?

I know little about diy co2, how long would a 2L pop bottle last?
And how do I know how to regulate the amount of co2 in the tank?

The constant checking to make sure ph doesnt swing too much?

excel just seems an easy solution.