This look ok for a biocide?

[aviduser]

Looking to pickup something local to throw in my distilled loop.

No More Algae from Jungle - Aquarium Maintenance - Fish - PetSmart

Also considering silver, but have no idea where I'd find some for cheap.

[MpG]

Actually, it just so happens that the active ingredient there is exactly the same as PT_Nuke - Copper sulfate pentahydrate. Now as for the necessary dosage, not sure about that. PT_Nuke is about 4% active ingredient, and requires about 1 drop/L. You'd have to check the concentration on the bottle and try to approximate it.

[Sadasius]

I don't know if I would trust an aquarium biocide just due to the unknowns. But silver is easily recovered from any custom jewelers in your area. Just get a piece and make sure it is large enough not to get sucked around the loop and make sure it's pure too. Like 99.999% pure. Drop it in your res and there ya go.