First time brewer's fermentation taking too long?

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May 25, 2022
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I'm attempting to brew kombucha for the very first time after watching a couple videos on Youtube. I got a SCOBY plus half a cup of starter tea from a neighbor and put it into a jar with tea made from 12 cups water, 9 tea bags, and 1 1/8 cups white sugar. I got some pH test strips about 10 days into the fermentation and it read about 4.5 to 5 in my estimation. Now at day 18, it is still around 4.5. Isn't this too high? Is 4.5 pH low enough that I don't need to worry about bad things growing in it? Is the lack of change an indication that fermentation has stalled?

On the other hand, the pellicle seems to be growing nicely; it has formed a thick new mat with a uniform color on the top. It tastes and smells like kombucha, but only mildly so. It is also sweeter than I would have expected. Am I doing something wrong? Did I have too little starter tea for 12 cups of tea? How long can I safely let the first fermentation go on for?

One additional detail: where I live, the temperatures have been fluctuating quite a bit, but I would say it has generally been in the 68-75F range in the house.

4.5 is too high.
4.2 is the maximum pH that you should start at.
Your ratio of starter to sweet tea was not correct. It should have been 20%.
You need to:
A. Add more starter.
B. Wait longer, let it ferment out and hope it doesn't get infected.
@rushpapers Thank you for the pointers! Unfortunately, I don't have access to more starter from the same SCOBY. Can I add some store-bought Kombucha (GT's Original) as a starter, even though it is from a different SCOBY?
I insulate and heat my 2.5 gal crock and like the time frame and acidity at 78*,takes 14-20 days and ends at 2.85 pH. I repitch 1 qt of booch into a 2 gal batch of sweet tea, and always the top new scoby. You don't need scoby to get a good ferment but I think it helps it go anaerobic sooner and have a milder flavor at that low pH.