I tried warming the kefir jar (and what was in it: water kefir grains + liquid) in a warm water bath, and later (after borrowing a thermometer from a neighbor - I have my own now) found that the temperature was definitely above optimal range (from what I understand this would be 75-80F). I continued warming the jar, but used cooler water, but the drink came out sour and I was told it was because the yeast had been more active or something.
Side-Note: I also saw some (not many) of the grains had brown spots (though I should mention they were eating nettle tea with Non-GMO Project certified evaporated sugar cane juice and organic molasses - this could have been the reason for the browning).
Has the yeast-bacteria balance been thrown off? If it has, how does one restore it? Can one?