Most of the answers to your questions should be in the documents I attached early on in this conversation. I use my lacto serum straight away to make a ferment so I forget the answers to your questions off the top of my head. I remember another use was for a compost activator.

Interesting about the old ferment pH rising a mate of mine had a stored rumen culture do the same. We suspect the culture has gone through the exponential growth stage past the sustained growth phase used up all the food and then gone to sleep and the pH has risen due to the lack of digestive activity. You should be able to split the culture 10:1 and start it again but I think splitting would be important to allow space for the exponential growth phase again.