Yay, it does look better!
Hopefully there's a light at the end of the tunnel too.
I try to avoid the gravel as much as possible, but if I do suck a piece up, I can remove a clog by pinching it. Easy and you don't have to stop the siphon or remove the line to unclog.
At least it's only another one, maybe two, more times with the airline before you get all the mulm out? All the water changes that you've been doing should also help with the ammonia spike.
After the visible mulm is gone and you return to normal siphoning, I'd suggest you take it easy
, no need to get too deep into the gravel, and definitely avoid uprooting any plants. The goal is not to get every last bit of gunk out of the gravel, but to get the surface accumulation, and just reduce it in general.
When you look for cories, check out the specific one Corydoras pygmaeus, the Pygmy Cory. They stay really small, school together and have the best little personalities. When I had a school of five in my nano, I was up really late one night and so they were up. One of them kept trying to sleep and the other pygmys would come over and nudge him or bounce on him a little as if to say, "come on! let's play!" Such cute little fish.
Now I want pygmy cories again!