They're not poor in nutrition. Just most fish don't like the taste of them. I've heard it said they taste bitter, but I have no interest in trying them myself to confirm. Best worm is anything that is not a tiger worm. Go dig around in your garden, whatever you find there should work fine.
I think 6.3 is about perfect for neons. But, yeah a handful of bird grit, oyster shells, coral, etc in the filter should keep the PH up. That's what I do. Though, I haven't tested the PH in about...Hmmm...5 years?
If you look around enough you'll find someone somewhere claiming anything will kill your fish. I read once that not completely defrosting your frozen bloodworms will kill your fish. Also, that you must use only clean water to wipe the tank glass because if you use spit some may get in the tank and effect the PH.
Channel doesn't appear to be registered with chanserv anymore. Probably was inactive long enough for it to be automatically deregistered or they lost the database? Easy enough to reregister it.
They look like tiny bristleworms. But those are marine of course. Very interesting, it's kind of sad that people with FW tanks don't cultivate all the little bits of wildlife like marines do.