I'll just say this.
The ocean is full of particles of all sizes. Rocks get worn down to sand. Sand is inert, and natural. Yet, if a sandblaster inhales a lot of sand, he can get silicosis.
The magic eraser is likewise inert, and small particles can be released. It is not natural, but unlikely it is much different than sand. With that said, it could harm organisms. Or not. Whose to say without some sort of evidence.
I do believe that organisms ingest all sorts of dusts and particles on a regular basis, be they man-made or not, and must therefore have a mechanism to cope with them. Our own lungs are protected by hairs, and mucous, to keep particle out. Is it a perfect system? No. Asbestosis and silicosis show that it is not. And they show that inert particles can in fact cause damage. Both asbestos and silica are natural substances, by the way.
In the grand scheme of things, I would conclude with no scientific evidence, that using the magic eraser is probably not harmful to tank inhabitants, any more than fine sand particles are harmful.
if you feel differently, then by all means choose not to use a magic eraser.