The pH of colloidal silver cannot be measured with a standard electronic pH meter.  This is because the electrode chemistry in the meter itself is based on silver/silver chloride, and these electrodes are known to read erroneously in solutions containing silver and other transition metals.  There is an electrode designed to measure pH in solutions containing transition metals like silver, it is known as a calomel electrode.  Calomel electrodes are based on mercury/mercuric chloride, and are not generally used because of the toxicity of mercury.

For the home user, an accurate pH reading of your colloidal silver can be made using Hydrion pH paper, which is only sensitive to hydrogen ions, and therefore is not bothered by silver in the solution.  Hydrion paper is available in different ranges, so make sure you get one which reads within a few units of 7.

There is a silver generator dealer who claims his CS has a pH of 10, and one of the members measured it with a silver based pH meter and it did indeed read 10.  He makes a big deal out of this claim probably so he can cash in on the alkaline water craze.  However the actual pH is no doubt less than 8.  Measurements of my CS are in the range of 7.2 to 7.8 using Hydrion paper which is accurate to .2 pH units.

Alkaline solutions feel soapy, slippery.  At pH 10, it should be noticeable.