The IPA I had was flawed. My last half dozen batches, right up to the Third Cousin has had a flaw that I've been trying really hard to track down. I've done ridiculous amounts of cleaning, sanitizing, made sure ingredients were fresh and have spent a few hundred replacing stuff. That IPA was soooo good until it carbed up. Then it had the same issue as several previous batches. I was only left with one thing, the CO2 tank. Until recently AirGas would fill your CO2 tank on the spot. But they changed their policy and you can either leave your tank for several days for them to fill it or you can exchange it for one that's already full. So I swapped tanks. Anyway, the tank I had been using on my most recent beers wasn't empty but I was so disappointed that the IPA developed the same flavor as my other recent batches and I had to keg the Third Cousin in time for the poker game so I went and swapped that tank out. For the first time in several months I have a beer that did not develop that off flavor. Ugh, I'm glad that **** is over.
It's not like the beer was undrinkable, but it has a very noticeable harsh aftertaste. I've heard that rust inside the tank can cause issues, so I'm thinking that's what it was.