Ah, the answer is in this HealthWyze article, which you will have to Google for because I can't link it.
" In batches that produce large particles of silver, because the electrolysis process is continued for too long, the voltage is too high, or the silver plates are too close together, some grayish chucks may form in the water. These particulates are actually safe and produced by the silver. They are especially beneficial for burns and skin infections, but they should be filtered out of the solution for internal use. A coffee filter works exceptionally well for this, and the solution may be drained by gravity through a coffee maker. Silver particles which have not clumped remain in either a colloidal or an ionic state, and these will pass through any filter."