Ok, sorry to keep asking the same thing - but should I put the carbon filter back in or not?
Todays water test: Ammonia 0, Nitrites .1
So the nitrites are down a bit. I think I will still do a 25% water change.
Good news is, the three remaining fish are doing lovely - active, great color, seem to be fine. Snails are better, although one is still quite sluggish. I check on him periodically and he responds quickly, so that is a good sign (I hope).
The tank also looks better overall. Thank you all for your help!