Alright so here is how you get CO2
dissolved into your tank.
Take this diagram...
on the left side of the image is the first option, a CO2
powered reactor. Takes up some room, kind of unsightly... not too many people use this method.
Second method is to build an inline co2
reactor. This is a good method, and popular if you have a canister filter. Basically, it would be hooked inline with your canister filter so all the co2
gets dissolved outside the tank. You get almost 100% diffusion (very efficient) and it keeps unsightly equipment out of the tank. You can also buy these commercially, but they are really easy to make, and cost only a few dollars to DIY, vs. a lot more to purchase off the shelf.
Here is Rex Grigg's step by step instructions on how to build the reactor pictured above:
How To Build A CO2 Reactor | Build a Regulator | Test Kit
The next option is to use a CO2
ceramic/gass diffusor. This is basically just a small attachment that you then suction cup to the inside of your tank. Small tiny bubbles are formed as the pressure from your system "squeezes" CO2
through the ceramic. They are not 100% efficient though, as some of the tiny micro bubbles will make it to the surface, escaping in the air, and thus not dissolving in your tank.
You can see the little micro bubbles coming out of the top of the disc...
The next method is called "the mist method". I used this for awhile. It is imo
the BEST method for plant growth/co2
saturation, but it has a lot of drawbacks. It can be noisy, and it causes a lot of turbidity in your water (the water will look cloudy from all the bubbles). The basic premise is that you position an airstone or glass/ceramic diffusor directly below the intake for a powerhead, which then sucks up the co2
bubbles, where the impeller chops them up into even smaller tiny micro bubbles that end up getting blown all over your tank. The bubbles are so small that the current keeps them from rising to the surface for a long time. As an added benefit, some of the co2
will get trapped directly under your plant's leaves where they can directly absorb the co2
during photosynthesis. My plants absolutely LOVED this method. Unfortunately, water clarity suffered. No real photos of this... just imagine the glass/ceramic diffusor pictured above situated directly under the intake of a powerhead... and lots of little tiny bubbles in the water column...
There are also lots of inexpensive ways to do this... but they can also be inefficient. You can just put a 70 cent airstone on the end of the co2
line and let it bubble in the water. Bigger bubbles means less gets dissolved into the water. Other solution is to use a "bubble ladder". The co2
flows up the ladder, and you can see the bubbles get smaller as they make their way up the ladder (as the co2
dissolves). However, a big ol' bubble comes off the top that then goes straight into the air (very inefficient). (see picture below)
Kind of blurry, but you can see the little co2
bubbles "climbing" the ladder.
Yet another way: A home made bell diffusor. Just cut the bottom off a plastic bottle, and attach it upside down in the tank with some suction cups, etc. Bubble the co2
line into it, and co2
gets trapped in the bell. Some co2
will dissolve in the water since it is trapped under the bell... however, this is pretty unsightly in a tank, and also inefficient.
I am sure there are countless other ways people have used, and probably even more that haven't even been thought of yet. The key is whatever works for your building skills, your time, and your budget. CO2
itself is cheap (whether pressurized or from yeast) so the process doesn't need to be 100% efficient. However, the more you get dissolved in the water, the more your plants are going to thrive (to a point of course... don't want so much that your fish suffocate!).
Hope this helps.
Good luck, and let us know if you have other questions.