Ive got a fairly old HDPE bucket fermenter. Ive noticed a bit of a rough spot on the inside for some time now. I never gave it much thought except for some extra cleaning with a rag before sanitizing. Well, my last two brews (particularly yesterdays) have gone into the bottle cloudy

. Taste was still good, but I must say that yesterdays bottling was
maybe a bit tart

. Its become evident I have an infection.
Cleaning up my bucket fermenter I notice that the "rough" spot had become much larger, AND that it was possible to scrape away the roughness with a finger nail

. I have always cleaned with a rag or sponge to avoid scratching.
I see two possibilities here:
1. Hard water scale deposits. We have very hard and alkaline water where I am. Is this possible with wort?
2. Bucket breakdown. Could the HDPE plastic be breaking down?
Ill be replacing my fermenter and adding an additional 1 or 2, but was curious if any of you have experienced a similar problem with plastic frementers.
"All I know is that the beer is good and people clamor for it. OK, it's free and that has something to do with it."
Bobbrews