A few links I found on colloidal silver. Would be interested how it pans out if you do decide to use it. Seems up in the air if it does impact the biological filter (although one company says not to dose in main tank - second link).
Seems as this was common before antibiotics in the 1940's.
Another idea would be to ask the person who suggested it for some useful links.
About Colloidal Silver | Active Colloidal Silver
Colloidal Silver for Fish - Dragon Colloids
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=26&ved=0CDwQFjAFOBRqFQoTCKj1-azUsscCFaPjpgodk0sBaw&url=http%3A%2F%2Fmedcraveonline.com%2FJNMR%2FJNMR-01-00001.pdf&ei=jijTVaj2NqPHmwWTl4XYBg&usg=AFQjCNGlGK83U82Q094Z3JyeG6yniBlfCQ&bvm=bv.99804247,d.dGY&cad=rja
Seems as this was common before antibiotics in the 1940's.
Another idea would be to ask the person who suggested it for some useful links.
About Colloidal Silver | Active Colloidal Silver
Colloidal Silver for Fish - Dragon Colloids
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=26&ved=0CDwQFjAFOBRqFQoTCKj1-azUsscCFaPjpgodk0sBaw&url=http%3A%2F%2Fmedcraveonline.com%2FJNMR%2FJNMR-01-00001.pdf&ei=jijTVaj2NqPHmwWTl4XYBg&usg=AFQjCNGlGK83U82Q094Z3JyeG6yniBlfCQ&bvm=bv.99804247,d.dGY&cad=rja