I've been fermenting my kombucha for about two weeks. After the first week my new scoby sunk to the bottom and a 2nd one began to form. It was still too sweet for me so I let it ferment some more. Now i see some dark marks on my newest scoby. Its a blueish black color but its not fuzzy and on the undersdide of the scoby. Are these just dead cells?
I think that the dark marks on the scoby are indicative of contamination or mold.
I haven't made kombucha for awhile but what I recall is that I had to feed the culture every few days. I remember that I had to reduce the brew by half and refresh with the same amount of liquid. So, if you have a gallon culturing container, after a few days remove half a gallon to drink or store and replace with half gallon of fresh sweet tea.
If the drink is too sweet for you, bottle the amount that you've removed and keep it in the frig for a few days. It will continue to culture, reducing the sweetness. Make sure you have room in the container for the gas that will be produced and remove any new scoby that begins to form before you drink it. You will have to honor the same cleanliness standards for this portion. Kombucha will always be a little sweet, even when the tartness begins to grow and masks the sweet taste.
I don't make kombucha any more because we don't eat any sugar any more (there will always be some residual sugar in drinkable kombucha) and it made too much. We couldn't consume enough kombucha to keep up with feeding the culture. I ended up pouring out a lot as waste in order to keep the scoby healthy. I tried making a smaller brew and it still made too much - additionally, with the smaller brew (about 1/2 gallon), the culture varied wildly, often becoming bitter or culturing too rapidly as the scoby grew even a little bit. There just wasn't enough "room" in only half a gallon of culture to maintain uniform culturing activity.