Starter strength and use in Levain

I have been trying to make Tartine's basic country bread. My starter is about 3 weeks old and I had been feeding it regularly with a 1:5:5 ratio (starter:flour:water) with a 50/50 mix of organic whole wheat and bread flour. It had been rising and falling predictably 5 days prior to me using it to make bread. It would smell "sweet and milky" after feeding and progress to an "over ripe fruit" smell, then have some vinegary notes later in the day/before feeding. I feed it once every 24 hours. I followed the tartine instructions and used 1 Tblsp of starter (I fed it in the morning and used it in the evening when it had an over ripe fruit/vinegary smell) mixed with 200 grams of the 50/50 flour mix and 200 grams water (at 73 degrees F). I let it sit overnight kept at 68-72 degrees F) for 9.5 hours. In the morning I mixed 200 grams of the levain with 700 grams water, 100 grams whole wheat, and 900 grams bread flour and continued with his instructions. I kept the rest of the levain as my starter to continue to feed. During the bulk fermentation my dough had an off smell I didn't expect. I expected a yeasty/beer-y smell or something like over ripe fruit but the smell was slightly unpleasant. I did end up with some gas bubbles. However, the new starter taken from the levain was fed the next morning and it now has an unpleasant sour cream/putrid smell that I associate with some kind of unwanted bacteria (leuconostoc?). This smell was present with a failed starter I had made a while ago. Did I increase the pH too much with the addition of that much flour and allow the bacteria to grow? If so, how do I make the levain work for making bread? Was my starter too weak to use in bread? Also, should I give up feeding this starter and revert to my back up in the fridge? Any input would be great.