Properly made Ionic Silver is .001 to .005 micrometers in diameter. That's 1-5 nanometers. Small enough for anything. Of course some don't want you to know this.
If you go above 20 ppm you will get agglomeration. Or you will have to use stabilizers which will make your product dangerous and inferior.
Toxicity. In this form of silver is so low that the water would kill you before the silver.