Yeast recipe
- Dissolve 400ml of sugar in near to boiling water in a pyrex jug.
- Add cold water to cool it down and end up with a lukewarm sugary syrup mix.
- Add 1 level teaspoon of yeast. Stir it in. I used sachets of bread making yeast from Sainsburys.
(My notes say 1 'small' teaspoon of yeast so it may well have been anywhere between 1/2 and 1 level teaspoon, it was a few years ago so I can not recall).
- Pour this into a a 2l bottle.
- Top up with cold water to about 1inch under the next of the bottle.
After a few days the mix started pumping out co2.
The mix petered out after 2 weeks.
I used to mix a replacement bottle 2 or 3 days before the 2 weeks was up and screw a lid onto it.
Leaving a yeast mix in an airtight bottle is potentially dangerous and NOT recommended.
If I left the bottle it would have exploded.
After 2 or 3 days I would unscrew the lid and switch it with the 'live' bottle.
Getting it into the tank
- Cut a hole into the lid of the 2l bottle just big enough to squeeze airline tubing into it.
- Make it airtight with a ring of blu tac (it works!)
- Inside the tank I connected this to a DIY barr venturi internal reactor (search barr report for the design).
I made mine out of an algarde gravel cleaner, a hailea hx-1000 pump, and a bit of airline tubing.
Switching co2 on\off
You can not switch DIY co2 off with a solenoid in the same way you with with a pressurised co2 setup, if you did the yeast mix will build up in pressure and eventually explode.
However by using the Barr venturi reactor I could place a timer on the pump to effectively turn the co2 on or off.
co2 would be fed into the reactor at all times, but when the pump was off it would just bubble straight out the top and dissipate. This gave the same effect as using a solenoid on a pressurised co2 setup.
The timer was set to come on in synch with the lights. Had I been a bit more knowledgable at the time I would have set it to come on a couple of hours before the lights on to get the co2 building up ready for the start of the photoperiod.
Reactor placement
The reactor was placed next to my fluval so that the reactors output was inline with the input of the filter.
By 6 hours into the day the reactors venturi would be kicking in fairly continuously.
When this happened I could see that all the bubbles being purged from the reactor were all being sucked into the filter nicely.
Patience
It took me about 5 mixes to get a combination of yeast that worked well. I ranged from almost no co2 out to quite high levels, but at high levels the mix only lasted a couple of days.
Along the way I gave myself doses of BBA, staghorn and string algae, presumably from unstable co2 levels. Plant growth increased right from the off which gave me good motivation to keep at it until I cracked it.
DIY Vs Pressurised Co2
The setup I have described here gave me good stable low levels of CO2. I was running 1.5wpg lighting at the time (T8 with DIY reflectors) so had low level lighting.
I ran with it successfully for about 6 months and then switched to pressurised.
I found the cost of sugar was lower than that of FE's, but not by much. If I lowered the output of my pressurised system to match that of the DIY then the pressurised system would actually work out cheaper in the long term.
For me it was a good exercise in proving experientally that co2 is good for plants (I was a noob and had to see it myself
). I coupled it with the EI system and proved to myself that I could grow aquarium plants successfully. It gave me a freedom to try new plant species without fear of killing them. If you know you are dedicated to the hobby already, and can stump up the initial investment for a pressurised system then I'd recommend doing that straight off.