Source of medicine after taste in all grain brew?

First time in about 40 all grain brews I have batch with a medicine after taste. It is a recipe I have made before with success. My water source is RO and there were no signs of infection when I bottled. Fermentation was in the normal range of 67 F using kolsch yeast (I had made this before using US-05). Not sure what might have happened and I am curious if anyone has any ideas. I would like to make this again but with better results.

7 lbs Vienna
3 lbs Pilsen
.38 Caraplis

0.5 oz Pearle (60 min)
0.5 oz Tettnang (45 min)
0.5 oz Tettnang (10 min)
0.5 oz Tettnang (5 min)

 

Hmm...from what I understand medicine like tastes usually come from chlorophenols; compounds which form due to chlorine in the water, or residual cleaner/sanitizer...since you are using RO water, it may have been due to improper rinsing...Ive also had a similar issue, and seemed to narrow it down to a combination of mash/sparge water pH being off, as well as sparging at a higher than normal temperatures

Could any of these be a possibility?

 

In addition to what Revelator said, could it possibly be chlorine from PVC leaching into the wort? Do you use vinyl tubing and such? Have you replaced it recently or no?

 

I think you may have confirmed what I suspected regarding sparge water either being at the wrong ph or too hot. I made two batches that day and the first batch was fine but this second one had the problem. I had a new thermometer to use and I had not seen if it was calibrated or not prior to use. I don't use tubing to transfer from my boil kettle to the fermenting buckets for 5 gallon batches, I just dump it in and go, but I will be sure to check/change the tubing the next time I do a 10 gallon batch.