this is based on designs i found online.

when i moved from a 10g planted tank to a 40g i found the bell jar method (upside down tumbler) wasnt efficient enough so i made this simple diffuser instead from the bits and pieces i had already.

basicaly i took an old gravel cleaner tube made some small holes (about 5mm) on one side near the bottom and just above them on the other side i made another hole. into the last hole the airline pipe, that comes from the co2 supply, is pushed in and an airstone is attached to the airline on the inside of the tube. below the holes a piece of course filter sponge, cut to shape, is pushed into the cleaner tube. this is to stop the dissolving co2 bubbles from being forced out the holes in the cleaning tube before they completely dissolve. personaly i dont use the filter sponge and i do lose a few small co2 bubbles but i find that the diffuser is efficient enough that i dont need the sponge. i get about 20-25ppm co2 in my 40g tank, if it was less i may have put in the sponge. attached to the top of the gravel cleaner tube is the input pipe from my fluval 204 external filter. this provides a fast flow of water into the tube that churns up the co2 bubbles and dissolves them. the holes in the bottom of the tube allow the water from the filter to flow back to the tank. instead of an input pipe from an external filter one could use a power head unit instead. ofcourse u would have to attach a filter sponge to the power head to stop fish being sucked into the power head.

one last thing, i use 2 filters on my 40g tank so the second filter is the one that provides the water flow around the tank as the flow that comes out of the diffuser isnt strong enough to provide much of a flow. instead of using 2 filters again one could use a power head or similar to create a flow of water in the tank, if required.

here is a diagram of my setup ...

Most Power-heads I've seen down here, come with Fish-Grills.

I reckon your setup's way more efficient than my Bubble Maze. My bubbles get smaller as they run up, but most do reach the top, and after a few merge, they 'burp' to the surface. Your setup traps the CO2, so it must diffuse. I've only seen the 'diving bell' (like your 10g) arrangement in most Internet CO2 DIY's.

Your wording of 'input pipe' kept throwing me, I had to reread. I always think of it from the Pump / Filters perspective (especially if I mention it). So to me its a 'Filter Outlet Pipe'. But I guess that happens when you grow-up, up-side-down, on the arse-end of the world!

Wheres the picture gone

this is one of the posts i hadnt gotten around to replacing the pic yet, but well just for u Clunk, consider it fixed.

Good man yourself