DIY CO2 Generator.

Yesterday afternoon I made myself a CO₂ generator from a fizzy drinks bottle and some left-over air line bits'n'pieces.

Dry stuff: Drill a 5mm hole in the bottle top. Slice the end of the air-line into a point and, using pliers, drag the air-line a few cm through the bottle top. This gives a good enough seal for the meagre amount of pressure generated. Shove the other end of the air-line on to an unused air stone.

Wet stuff: Dissolve 1½ cups of sugar in a jug of water. Add the water to the bottle and top up to about ½ full (or ½ empty if you're feeling pessimistic). Shake well. Add 1½ tsp of fast-acting dry bread yeast and shake well.

Stand the bottle somewhere suitable, put the air-stone somewhere suitable..... and wait.

Remember; the CO₂ has to displace all the air in the bottle before it gets in to the water, so it will take a while.

IMPORTANT BIT: There is absolutely no control over the amount of CO₂ generated this way and it is entirely possible that it may cause a pH crash in your tank. You do need to be well up on the relationship between pH and KH and how this affects the CO₂ content of your water, and have test kits for both pH and KH. Dissolved CO₂ chart here.

I'd only got a short bit of air-line so this isn't the final resting place if I decide to keep it. However; as this is the hardware section of the forum I'll discuss the efficaciousness (or otherwise) of the CO₂ addition elsewhere.

If the bottle is below the tank then an in-line non-return valve would be a good idea.

DISCLAIMER: I am no way responsible for the sticky mess that may ensue from any attempt to recreate the above contraption.

And, before you ask.......

I use the green tub. You have to 're-activate' the yellow tub yeast. As I make a lot of bread then the green tub can be kept in the fridge as I get through it quickly enough before it goes stale.

I assume at some point you'd have to either top up with sugar or add more yeast?

Yep! Although I'll probably just get another bottle started and swap them over.