what parts are u running?
this is totally dependant on what metals u have mixing in your loop.
Silver takes time to work also.
Its not a BAM instant Fix solution.
The coolant needs to be in contact with silver for some time for the silver ions to leech into the water.
Usually the time for algae to grow is longer then the time required for silver.
However u cant expect silver to fix a system right away...
(dropping it late into an already setup water system, because once u got growth, the silver wont outpace it.)
Additives offer corrosion resistance.
This is very important if ur mixing metals.
Copper + Alu => spell for destruction if ur not running an additive.
Now we are in winter, the room temps are 18-20 degrees C, during the summer days (jan-mar/apr) the temps (room) are about 26/27 degrees C. The biggest problem here in Peru (especially Lima), is humidity, during the year (lowest/summer 80%, and highest/winter 98%).Distilled water and a silver coil worked great for me when I had a real water cooling system.
If your paranoid you could always add a drop or two of PT nuke I guess.
How is the weather down in Peru? High ambient temps?