Welcome back! Last month I described a method for generating CO2 using a pop-bottle with some yeast and sugar water, this month we'll build a reactor to get the CO2 into your tank water.
This CO2 reactor works by using the impeller of a powerhead to smash the relatively large CO2 bubbles into millions of tiny "bubbletts". These tiny bubbletts must be held underwater long enough to allow them to be completely absorbed by the tank's water. This is accomplished by feeding the output of the powerhead into a cylindrical bottle. Inside the bottle the water swirls around in a cyclone-like manner which causes almost all of the CO2 to be absorbed by the water. The output of the bottle is then sent through some 1/2" tubing down below the substrate and to both ends of the aquarium.
To build this reactor you'll need the following items:
The powerhead can be obtained form your local pet store or favourite mail-order aquarium supplies place. The plastic bottle is the type used as a hamster water bottle. It should be about 4-6cm in diameter, and have straight walls approximately 15cm long. The inside of the mouth of the bottle should be about 1/2" in diameter so the poly tubing will snugly fit inside. The remaining items can be obtained from your local hardware store. Be sure to buy only aquarium-safe silicone.
Using a carpenter's knife or a sharp pair of scissors, cut a 1/2" diameter hole in the wall of the plastic bottle. The hole should be within 1cm of the bottom (ie the end without the opening) of the bottle. Use the sandpaper to roughen the bottle's surface around the hole. This will help the glue to stick to the plastic.
With the carpenter's knife cut the end of the 1/2" poly tubing at an acute angle of about 20-30 degrees. Roughen the tubing's surface around this angled cut. Next, cut the tubing to a final length of about 8-10cm.
Push the tubing into the hole in the bottle. Orient the poly tubing so that the water entering the bottle will spin, thus forming a cyclone. Attach the poly tubing to the bottle using hot glue followed by silicone to ensure it remains in place.
While the silicone is curing we can plumb the tank. Cut two pieces of poly tubing approximately half the length of your tank. Attach the two pieces with the poly "T", and insert the elbows in to the opposite two ends. Hide this piping under you substrate near the back of the tank. The "T" should be pointing up, and the elbows should be pointing forward and slightly up.
Next cut a piece of tubing to connect the output of the plastic bottle to the "T" connection. The end of the bottle, with the poly tubing glued to it, should be about 2-4cm below the surface of the water when finished (this will be dependant on the type of powerhead you have - since the output of the powerhead needs to be fed into the bottle).
Connect the output of the powerhead to the input pipe of the plastic bottle. Properly mount the powerhead (don't just let it hang from the pipe). Using an elastic, strap the 1/4" output tubing of the CO2 generator to the intake of the powerhead. Mix-up some CO2 brew and you should be up and running as soon as the yeast becomes active.
One final thing which is helpful is to drill a small hole in the top of the cyclone chamber (this is actually the bottom of the bottle - confused yet?). The hole should be plugged with a small plastic screw which can be removed to vent any air out of the bottle - useful initially, and after water changes.
That's it for another month! I hope you have as much fun tinkering with your tank as I do - bye for now...