Ive been looking for some KN03 and this seems to be a good resource:
http://www.aquaessen...products_id=522
they use paypal and nochex so its not going to be logged on any credit cards etc.. just incase..
That's very strange for an aquarium shop to sell a nitrate fertiliser, the fish themselves produce far too much nitrate (via ammonia) which often needs removing by water changes, as even a very heavily planted aquarium tends not to remove it all. And seeing the nitrate is toxic to the fish themselves it seems bizarre to add it to the tank.
As this is hugely off topic, something relevant:
It seems the vast majority of the ebay listings for KNO3 are only selling garden direct material anyway, so you may as well go straight to GD, or another company, that I'd be wise not to mention or my delightful insight into fish will be removed.