Nemo wrote in message
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Second time I've tried this now with no luck.

- 1 well rinsed 2L Pepsi bottle
- 1 cup sugar
- 2 cups of warm-hot water to dissolve the sugar
- 4 cups of cold water : result is 6 cups luke warm sugar water
- 1 tsp baker's yeast (stored in the fridge)
- half a dozen shakes

I have a check valve in the line to prevent the tank water from siphoning
back into the bottle.

I get foam at the mix's surface but no sustained CO2 after 24 hrs. It
seems
as if the culture just dies off after it gets started

Tap water parameters a

pH ~ 8.0
gH ~ 3
kH ~ 2-3

In the second attempt, I used chlorine-chloramines remover in the water to
no avail.
The temperature in the house goes down to 16-17 oC during the day this
time
of year. Could this be the problem? Do I need to insulate?

Don't worry about air temperature. It may slow down CO2 production but will
not halt it altogether and will certainly not kill the yeasties. Assuming
the water is not too hot - over 110º - when you add the yeast, you have a
leak somewhere in the system.

I'll bet you a quarter it's leaking where the airline fits to the check
valve - sniff there and see if you can smell it.. I never use check valves
anymore. I just put the bottles up on the back of the tank (where they are
warmed by the lights) with the shortest possible line straight-shot into the
tank - one end siliconed into the DIY bottle, the other under water, nothing
in between.

If not at the check valve, sniff at the cap itself to see if it's leaking
out the screw-on bottle cap threads.

Remember, the CO2 gas has to build up enough chamber pressure to overcome
the pressure of the water it is entering. Even the most miniscule leaking
in the line is enough to lose most of your gas. I have had any number of
bottle rigs leak over the years. Some just never were any good and I never
figured out where they were leaking from but just had to replace anyway.
Quite often I have to reseal an airline into the bottle cap because the
pressure of repeated twisting has loosened the seal.

Good luck.