I agree one shrimp will likely not be enough. You might also consider adding pure ammonia. Use pure ammonia without surfactants (available at most hardware stores, I get mine at Ace Hardware) or perfumes. To be sure the ammonia does not contain surfactants shake the bottle and if it bubbles up like dish soap it has surfactants in it, pure ammonia will not have bubbles. To raise 100 gallons of water from 0 to 2 ppm ammonia you would need to add 0.8 grams (8 ml) of standard 10% pure ammonia.