So I went to my local aquarium store, all stoked to pick up some aeration equipment, and was a little disappointed. Instead of an inline HEPA, I've got a built-in unspecified filter in my air pump and the grace of G'd to rely on for sterility.
I've set the pump intake on top of the out-vent of my home HEPA filter, and I'm 24h aerating a starter on a Wyeast 1968 (Fuller's) ESB yeast, with the incremental feeding and all as per Roving Brewer. Right now the smells coming out are great - healthy, wonderful bread-dough scents - but I recognise the very real chance of an infected starter with this McGyver'd setup.
I'm pretty certain it's healthy now - what should I be on the lookout for? Vinegary smells, I know, could mean a problem, and lacto, lambic scents will scare me. Any other good indications of starter health? I plan to improve this setup, obviously, before I risk spoiling a special-ordered yeast or a really exciting beer, but in the meantime - what do you think, guys?