new quarantine tank set up

Dear hobby:

Not to worry — the odor you have noticed commonly occurs when you are using the fishless method of cycling a new aquarium and is usually short-lived. It indicates that the decaying shrimp is producing plenty of ammonia to feed the beneficial nitrifying bacteria, and as the population of Nitrosomonas bacteria that feed on the ammonia increases, converting more and more of the ammonia to nitrite, the fishy stink will diminish and disappear.

As you know, when using the fishless cycling method, it is standard operating procedure to add raw, uncooked cocktail shrimp or prawns to the aquarium, and to leave the decaying shrimp or prawn in the tank throughout the cycling process so that it can provide ammonia to feed the beneficial nitrifying bacteria that carry out the nitrogen cycle and provide the biological filtration for your aquarium.

When cycling a new aquarium, you must first seed the tank with beneficial bacteria, which is usually accomplished by adding live sand and/or live rock, and then feed those bacteria with a source of ammonia so that their population will grow as much as possible. If there is no ammonia in the tank to sustain them, the population of the good nitrifying bacteria will begin to die back or starve, so you also be to add a source of ammonia to your 10-gallon quarantine tank to keep the population of beneficial bacteria growing and thriving. There are a number of different ways to feed the beneficial bacteria that will be providing the biological filtration for your aquarium with ammonia.

Some hobbyists use hardy, expendable fish, such as damsels or mollies to feed the bacteria with their waste products, but you are using the fishless cycling method that I prefer (well done!), which involves adding a piece or two of uncooked cocktail shrimp (i.e., prawns) or similar biomass to the aquarium, which will produce abundant ammonia as it decomposes.

The only drawback to this method of cycling is that it can sometimes produce an objectionable odor nearby the aquarium as the cocktail shrimp/prawn decomposes. Most times this just produces a slight "fishy" odor, but sometimes, in the advanced stages of decay, the odor of putrefaction can also become quite noticeable. If it gets to the point where it’s driving your hubby and kids out of the house and mutiny is in the air, then you may have to remove the decaying shrimp and explore other alternatives. If your new quarantine tank is getting really stinky, you may have added a little too much shrimp for a tank of that size. If you can wait it out, the stench is only temporary and will begin to diminish as the population of Nitrosomonas bacteria increases and converts ammonia into nitrite. If the offensive odor is too bad to wait for it to diminish and decrease naturally on its own, then you may have to remove some or all of the decaying shrimp.

If that proves necessary in your case, hobby, you can use another source of ammonia instead, such as a few mollies. Or you could try adding ammonia to the aquarium directly, drop by drop. I can provide you with instructions for the latter method of feeding your biofilter if you would like to give that a try. Let me know if you can ride it out, or if the odor is becoming overpowering and you need to switch methods quickly.

Best of luck cycling your quarantine tank!

Respectfully,
Pete Giwojna