I have a 4 and a half inch pleco in there with him. Could it be possible he is a suspect?
Yes definitely if the Pleco is not properly fed then it is quite likely to start sucking on other fishes slime coat, ganoid scaled fish like Bichirs in particular as their slime coat is thicker and more nutritious than on many other fish. A lot of people here will tell you to never even house Plecos together with such fish because of this, as a compromised slime coat usually equals a dead Bichir.
Your tank also seems to be free of both plants and algae, which means that your pleco is not only lacking protein but is also seriously hungry otherwise. Most common species of Pleco have high metabolism and grow quite fast in the right conditions, and will need a much more varied diet than thin sheets of green algae.
I've never seen what this looks like in person, so I can't say for sure, but now that you mention the Pleco I would move the bichir to a seperate tank and treat with salt right away, then hope for the best I guess.