Once you get a feel for the length of time your mixture produces CO2, establish a regime where a second bottle is started before the first one putters out, then alternate them. My system uses four 2-liter bottles to hold batches of mixture piped into a bottle half full of water, then into an empty bottle that discharges CO2 into the tank or an air system.
My equipment:
• One-eighth-inch airline tubing
• Four 2-liter bottles with caps
• Silicone aquarium caulk
• Airline fittings (optional)
Setup:
• Two mixture bottles, each with one airline coming out of the cap. Disconnect, and valve airline into bubble count bottle.
• One bubble count bottle with two airlines coming into the cap from the mixture bottles, and one airline going out of the cap into the sump bottle.
• One sump bottle with one airline running into the cap, and one airline going out to the aquarium or air system.
Take two of the bottle caps, and poke one hole in the top of each of them; either put the caps in a vice and use a drill, or heat up an old Phillips head screwdriver and melt a hole through the top.
Take the third bottle cap, and either poke three holes in it or one hole large enough to fit three airline tubes through.
Take the fourth bottle cap and poke two holes in it, or one hole large enough to fit two airlines through.
Use aquarium silicone to secure the airlines to the caps and to create an airtight seal. Avoid getting the silicone in the threading of the caps.
If your mixture lasts strong for two weeks and keeps producing, albeit slowly for a third week, start your new bottle at the end of week two, and alternately change bottles every two weeks. The goal is to keep the sump bottle empty.
Caution: Don't burn the palm of you hand or let a bit of plastic fly into an unprotected eye. Also, you are dealing with containers holding gasses under pressure — if handled improperly or a valve is not opened, one of the bottles may rupture.
To measure the amount of CO2 your system is producing, extend the inbound airlines of the bubble count bottle to within 2 inches of the bottom of the bubble count bottle. Fill the bubble count bottle halfway with treated water (chlorine and chloramines removed), keeping the outbound airline well away from the top of the water. That way, you can count the bubbles.
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