Anything much beyond 20ppm is not necessary for CS to be effective. The 100-10,000 ppm stuff you see in the healthfood stores is a waste because in order to get the ppm that high you have to use animal protien to keep the silver suspended in the solution. This lessens the bioavailabilty of the CS so nothing is gained. The best CS that can be made should be clear with the smallest particle size. This can be done by using current control which lowers the current when silver concentration increases. Units with current control like the Silvergen or Silverpuppy have this feature. There are probably a couple of more units out there that have this feature as well. You probably could build a CS gen with this feature if you are electrically inclined. I use a Hanna PWT meter (about $60) to get a rough indication of ppm.