Co2 for YOU! Cool co2 maker/storage (uses BakingSoda+Citric acid)

Been using this cool little CO2 regulator/device (great for small grow rooms). Fits any standard 1.5/2 litre bottle (screws straight on). Ordered from China via Ebay and took 2 weeks to arrive (but cost £20 including delivery). I'm finding it stretches you baking soda/citric acid mix a long way and makes it easy to adjust.
You could make it yourself but i hadn't seen this device shown in any threads so i thought i'd post it:

http://www.ebay.co.uk/itm/360696423683?_trksid=p2060353.m1438.l2649&ssPageName=STRK:MEBIDX:IT


Heres are two videos of it in use

I've used this for a time now and can say on average it lasts around a week (dependant on what release rate you have set and that you turn it off at night, naturally).
Fyi - i submerged the pipe under water and counted the bubble rate in order to calculate what i wanted to give my plants.
Also, once you get happy with the proceedure you can add a lot more baking soda to the baking soda side ..but hold back on adding that much more then an egg cup full of water to it. This allows you to add more citric acid+water to the other bottle (thus extending usage time, as its the citric acid side that drains into the baking soda bottle).
Or, just get larger bottles (i use two 1.5 liter bottles but 3 liters or more could be used - if the bottle mouth is the same size). Or, use two differing size bottles in order to extend life ...experimentation is the order of the day!