Those definitely weren't monti polyps but you're right, they looked similar!
I will say that your progress is good. And FYI, I had a local club member with your same problems you had a month or two ago. I told him the same thing, the chaeto was stripping his water sterile and stealing all the trace elements that SPS need. Based on your success I suggested a light dosing of Fuel. His tank has improved dramatically and is taking off again.
The chaeto was his problem.
I will say that your progress is good. And FYI, I had a local club member with your same problems you had a month or two ago. I told him the same thing, the chaeto was stripping his water sterile and stealing all the trace elements that SPS need. Based on your success I suggested a light dosing of Fuel. His tank has improved dramatically and is taking off again.
The chaeto was his problem.