Carboy cap oxidation?

[Smelletor]

Am I completely paranoid in worrying about oxidation from using a carboy cap/blowoff tube into starsan setup as my airlock? I'm worried because sometimes when the ferm is really chugging I won't see bubbling until I clasp my hand around the carboy cap. Also, since I'm crash cooling, I'm thinking it might be sucking some air into the carboy if it's a bad seal.

[TheDarkSide]

Never had a problem with that or got any dings on competitions and I've been doing it this way for a couple years. As long as the hose stays below the star san level, it should be good.

[dstar26t]

I put 2 o-rings (mcmaster #9262K325) below the carboy lip before installing the carboy cap. It seals much better, especially when using a zip tie. I originally got the o-rings as sanke spear o-ring replacements but they weren't quite exact. Slightly too thick and slightly smaller ID than the sanke o-ring.