I batch brew 3 gallons every 8 days. Boil one gallon. Add 1 cup sugar and 8 tea bags. Usually use a combination of Green, Black, and Oolong tea. Get the benefits from all. Let cool then add to gallon jar with scoby and one cup starter.
Bottling during second fermentation I add one teaspoon...
I haven't used those type of bottles but many do... After a few days during the second ferment tilt the bottles slightly and see if any are leaking. If so then you know some of the carbonation is leaking out also.
Might need a little more info...what type of bottles are you using for second ferment, seals, etc. Are you adding flavorings to second ferment?
How does your brew taste before bottling for second ferment?
Just guessing but I suspect your bottle seals could be the issue. Some of my caps are...
Try adding a little sugar directly to the bottles during second fermentation. I generally add a teaspoon or so then a little of the new brew and shake the bottles a few times to dissolve the sugar. Add flavoring then fill on up. The yeast will still eat up the sugar during second fermentation...
We've been using frozen concentrate juices. Cranberry is our favorite. Pineapple and apple is good also. I usually add 3-4 tablespoons of the concentrate to each bottle. A little more with the apple. I've also used a few slices of fresh ginger root.
All added when bottled during secondary...
From a web search....... Companies need to suppress or halt yeast fermentation and culturing in order to prevent continued carbonation or the bottles could explode. This process leaves you with commercial kombucha which, while still good, typically has high acid and/or suppressed culture, and...
1/4 teaspoon of sugar is probably a little light. I bottle 3 gallons weekly using batch brew. Depending on the tartness of the brew I add 1 teaspoon or even a rounded teaspoon to each 16oz bottle.
I add the sugar straight to the bottles then add about 1/2 cup of the new brew. Shake the bottles...
I've been brewing for a little over a year now and felt my brew was getting a little too vinegary so my last batch I have filter the brew through a cheese cloth prior to bottling. I also cleaned a little of the yeast from the scoby.
I believe there is still plenty of yeast left in the bottles...