Originally Posted by toofazt
I've had best results using an in tank reactor. You just get a little powerhead and hook it up to ~6'' plastic tube and stuff some coarse sponge material in the end of the tube. You feed the CO2 line into the powerhead, the powerhead chops up the bubbles and shots them into the tube to diffuse...
This is a shot of my DIY diffusor. Similar theory except I've modified the powerhead to take the co2 tubing into the inflow and get the gas munched up into even smaller bubbles. That's in the top right corner (it's a bit hard to see the tubing.
From there it feeds into an old garlic crusher I had lying around. I've drilled one hole in the larger chamber. A small section of airline allows any major buildup of gas to escape. A bit with small holes in seperates the large chamber from the smaller bottom section which has had a number of smaller holes drilled in it to allow the co2 enriched water to escape. I did have a small bit of sponge in between the two chambers, but removed it as it really didn't do much and started to build up with gunk.
This is still running in a 150L (40 Gal) tank, with 2 x 2-litre bottles of SYM (sugar-yeast mixture). It gets me co2 levels of around 22ppm. The powerhead is a Rio 300l/h job (not sure of the model number but they're ultra-cheap usually).
Just an indication of how you can use your imagination. I'm sure using the gravel vac tube method works equally as well. But, in the name of DIY, this is what I had lyting around unused.
(Btw, this is view from the back of my tank - it's an inbuilt)