Black Rust

[jcali10]

I got rid of the BGA I had a short time ago in my 50G. Then I modified my dosing regime; I started using a 3:1:3 NPK mix, and I dose magnesium and CSM+B also. I have what appears to be black rust on the leaves of some plants. Most noticably on a few of the C. Wendtii leaves.

Is this a form of BBA?

Am I overdosing something maybe?

Not sure what my next step should be.