Colloidal Silver goes "bad" when the particles fall out of solution because of exposure to light, or extremes of heat or cold. If Silver Colloid turns dark, it is in a more irritating oxidized form. I commend making fresh Silver Colloid with distilled water using two 99.99 FINE SILVER WIRES and three 9 volt batteries connected in series, red-to-black to get 27 volts. In short, there is no reason to rely on expensive commercial Colloidal Silver . You can make it for pennies a gallon!
Email me at: nordskoven@yahoo.com for instructions if you like. I get my 99.99 FINE SILVER WIRES, 14 gauge, at C.C. Silver & Gold, listed on the net. I just send them a check and tell them to forward whatever length of wire it covers so I avoid going back and forth getting quotes. Use scraps of FINE SILVER WIRE, NOT STERLING, in filters to avoid slimy scum inside the filter tank.