possible stem problem!!!!!!!

Ive got a hydro set up, everything is going cool with all the plants but one looks like there might be trouble ahead..... the base of the stem is a lot skinnier than the rest of the stem, it doesnt look like its molding or anything but almost as if a beaver came along and gnawed it down a little... theres no bugs or mold or growths or anything anywhere in my tent i keep it pretty clean... heres a picture please let me know if i have something to worry about!!!



thanks for the help!

thats called collar rot , you never wanna keep your stems wet.your plant is either to low or your medium is to high

Thanks for the help, I have had my medium too high but I adjusted it recently. Is there any way I can stop the rot/heal the plant/anything posative?