more starter shenanigans - starter acidity

I have a 100% hydration 50/50 whole wheat and white flour starter. A while back, I was having trouble maintaining its health. No matter how faithfully I'd stick to feeding schedules, it would develop a weird rotten egg smell. I believe that this was due to discarding too much of the starter every time I fed it. The acidity that was making the starter "immune" to colonization by unwanted bacteria was being diluted too much.

The fix was easy - I now feed at a 1:1:1 ratio of starter:flour:water, and the rotten egg smell is gone. However, leavens that I use for things like Tartine BCB require only a tablespoon of starter. After an overnight ferment, they do start to develop a bit of the sulfurous smell. I am kind of baffled. All signs point to the fact that I have a healthy starter (smells pleasantly acidic, doubles on schedule, no hooch or other signs of deprivation), but it seems quite sensitive to other things floating in the air. Any words of advice?