I'm aware that DIY yeast CO2 isn't the most popular topic in the forum, but just in case there is any I nterest I have an update on the Mk II yeastulator.
This system has been running for nine months now and I have been gently tweaking the yeast mixture to find the optimum that gives the longest sustained time between refills. This is a mix that gives more than enough CO2 and a good long maintenance interval.
Firstly, It is running on a 300litre tank which is normally said to be well above the upper limit for yeast systems because they 'cannot' generate sufficient CO2 or just take too much effort.
This mixture and the system in the link can easily achieve a stable day/night timed 30ppm CO2 level without adjustment for 6 to 7 weeks between yeast refreshes. I had found that a normal yeast setup on smaller tanks generally needs a partial change of the yeast every week and constant tweaking and this is why most people give up on yeast. Well don't, it much better than you think!
The quantities I have are for a 10litre yeast mixture (warning ! DON'T consider trying this quantity of mixture unless you use the storage/regulator system in the link)
The base is a brewing yeast, I have tried several brands and they all seem work equally well.
Feed stock is 2kg of normal white sugar, dissolve 500gm at a time in 1litre of boiling dechorinate water (1 drip of declorinator per litre)
Because I have very soft water I also add 1 spoon of bicarbonate of soda in each sugar mix. (4 level teaspoon in total)
Add 3 level teaspoons of yeast to a small quantity of warm water with a sprinkle of sugar to kick things off while you dissolve the sugar - don't add it to the sugar solution just yet.
The 10litre container will now have 4litres of very hot sweet water in it and would probably kill the yeast so add an equal quality of declorinated cold water to bring it back down to a pleasant 'babies bath' warm.
Then add the yeast mixture which should be starting to foam, and finally top up to 10litre leaving just a small air gap to prevent the mixture being forced into the tubes.
The mixture will be producing a good quantity of CO2 in an hour or so, but because the storage system is also a pressure regulator it should not require any adjustment, just check it the following day to confirm the header tank is filling up.
I have not found that the mixture needs shaking and I just ignore it only checking the header tank weekly to know when it starts to run out.
I have two yeast containers so while one is in use I leave the other filled with a water chlorine mix so it is clean for the next refil. This whole process takes less than half an hour, job done.
https://forums.thinkfish.co.uk/fish-tank-plant-advice/pressure-regulating-a-diy-co2-system/