Hi! I'm so sorry and I hope your fish get better. Im no expert, but in the past my clown knife developed something similar. Looks like cloudy eyes to me. I think the culprit is parasites from new fish additions since you stated that water quality is good. I would probably use API general cure or some kind of parasite killer. Again not an expert and also a new bichir keeper just wanted to chime in! Good luck, your additions look so cool and again so sorry this had to happen.