Why Carbon?This is extremely unfortunate but YOU killed the tank WITH chemi-clean. I think that’s where people get it wrong. I have used it, as have others, with no issues at all.
Did you clean out as much of the cyano out as possible before dosing the tank?
Did you over oxygenate your tank while treating your tank?
At the point you are at now I would’ve tried doing the largest water change possible and adding carbon.