Hi Cruise Control. If you are referring to the office tank, I only use 1 bottle. I usually change after 10 days and use 2 cups of sugar, 1/2 teaspoon of dry yeast with 1/2 teaspoon of baking soda.

The 2 feet tank at home which you see in the photos are using pressurized CO2 tank while my 2 feet moss tank also uses 1 DIY bottle.

Here's a tip which may be helpful if you use DIY bottles. Mix your yeast with some warm dissolved sugar (1/2 cup sugar) in a cup first. The reason is to test if the yeast is still alive. After a while (about 5 minutes), when you have seen foam surfacing, then pour the whole solution into your dissolved sugar in the bottle. My wife taught me this. Apparently, it is a baking tip.

Oh yeah, another useful tip. Never share sugar and yeast with a wife who likes to bake.