repeating what djlen and I have already said, you really don't NEED co2 unless your WPG is 2+. Hairgrass needs quite a bit of light so i'm gonna assume that you have proper lighting
Here are the instruction for the way i used to do my DIY co2 along with a DIY bubble counter.
DIY CO2
Parts:
screw (the type i used are spax 14x1 1/2 or 6x40mm)
screw driver
needle nose pliers
two juice bottle (i used 2 liter cranberry juice bottles)
box cutter
air/co2 hosing (co2 hosing is a little stiffer easier to force through holes without breaking)
diffuser
powerhead (optional)
one of those t fittings that let you plug two air tubes in with one outlet
check valve (for each bottle you use) brass is better but plastic will do. (any petstore wll have these)
RINSE ALL THE BOTTLES AND CAPS!
1. Put a screw to the cap and screw it through to make a whole. Be sure to use a screw that will make a whole slightly smaller than the air tubing. (you'll see why in a minute)
2. Cut the airline tubing at an angle.
3. Place the longer/skinnier part of the tubing through the whole in the cap,
grab onto it with your needle nose pliers and PULL (by making the whole smaller and forcing the tube through, you will ensure a good seal between the cap and the tubing)
Cut the tube so that about two inches remain in the bottle.
4. Repeat for second bottle, or how ever many you desire. I suggest two until you figure out how it will effect the water.
5. Place a check valve on each of the tubes coming out of the bottles and then finally plug them into the T fitting.
6. Plug a single line from the | end of the T fitting that will run to the tank.
7. If you choose to make a bubble counter, it would go AFTER the T fitting, if you do this, you do not need the two check valves before the T.
8. Plug the line into a diffuser of your choice, I like the mighty momato we discussed above.
9. For best results place the diffusor under the intake of a filter or power head (more swooshing around forcing more co2 to dissolve in water.)
10. AND YOU ARE DONE!
The Recipe!
Ingredients:
Bakers Yeast
Sugar
Baking Soda
Water
1. Put two cups of sugar into the bottle.
2. Fill the bottle 2/3 full slowly as to not disturb the sugar on the bottom with luke warm water. (Not too hot, it should feel warm to the touch)
3. 1/2 teaspoon of yeast
4. 1/4 teaspoon of baking soda
5. Put the cap back on and you are done, you should start seeing bubbles within the first 12-24 hours. This lasted me about 30 days.
The Bubble Counter
Parts:
Check Valve (again, any pet store will have these, same ones as for an aquarium air pump)
Oral Syringe (you can find one in any pharmacy store such as rite aid)
Adhesive (believe it or not i used jbweld)
SMALL rubber band
1. Pull the syringe apart. (take the plunger end out, it should just come apart)
2. Place the rubber band or the seal from the plunger around the checkvalve to give you an idea of how far down to place the check valve. (and to keep the adhesive from getting inside.
3. The syringe comes with a plug, leave it in the small end and fill it halfway with water.
4. Place the check valve inside the wide syringe end. Some will fit snug while others won't fit, that is why you use the rubber band... to give it more diameter.
5. Apply the adhesive to the checkvalve/rubberband/seal, whichever and let sit for the night.
It should be dry by that point and since there is a check valve there... you really don't need the two before the T.
6. Plug the line coming from the T into the bubble counter and another tube onto the top of the bubble counter to the diffusor.
DONE! Sorry I dont' have pictures for this one but I can't find my bubble counter.