#### vauxhallmark

##### Member

- Joined
- 29 Jan 2008

- Messages
- 570

I have suspected that it was very efficient for a while, because of the size of the bubbles that reach the top, but I couldn't remember the formula for the volume of a sphere (shame - it has been (ahem) a few years though..).

If you've never used one, you probably know what they look like (big and ugly), but if you've never seen one in action, this is what happens:

A bubble of CO2 enters at the bottome of the ladder. It's about 8mm in diameter.

It travels left and right up the ladder, shrinking as it goes (and the CO2 dissolves). As it shrinks it travels more slowly, so at the bottom you have a few big bubbles, and at the top, loads of bubbles which have shrunk to between 1.5 and 2mm.

A 2mm bubble doesn't sound that much smaller than an 8mm one. Even a 1.5mm bubble doesn't sound

*that*much smaller than an 8mm one. But I knew that the formula for formula for volume of a sphere (eg bubble) included a power of 3, and would help me calculate how much CO2 was dissolving in the aquarium water and how much was being wasted.

Here's what I found (thanks Wikipedia !)

The volume of a sphere is 4/3 x Pi x r^3 (4/3 x Pi x r x r x r) - I'm trying to say 4/3 Pi r cubed, but I don't know how to type it.

I can't be sure whether the bubbles that finally reach the top of the ladder are 1.5 or 2 mm in diameter - let's say they're 2mm.

Therefore the volume of a bubble of CO2 entering the ladder is 4/3 x Pi x 4mm^3 =

**268mm cubic mm**.

The volume of a 2mm bubble at the top of the ladder is 4/3 x Pi x 1mm^3 = 4

**.19 cubic mm**.

That means 4.19 cubic mm is 1.56% of 268 cubic mm. so

**98.44%**of CO2 has been dissolved in the aquarium water - result!

if the bubbles are in fact 1.5mm in diameter when they reach the top that would mean that

**99.34%**of CO2 had dissolved in the tank water.

Obviously the choice of diffusers is wide and personal these days - I'm just posting these observations so that if people have a set up that could accommodate this kind of diffuser (probably either a grow out tank where looks aren't too important, or a tank that allows you to fulfil the opposing criteria of hiding a big ugly diffuser, and making sure that it receives enough current to circulate the dissolved CO2 round that tank) this humble bit of plastic could be a good way to get the most out of your CO2 bottle.

M