The ammonia cycle

Setting up your first marine tank can be an exciting, yet daunting time…..

You have made the decisions on circulation, lighting and hopefully the filtration method and its time to bring it all together.

Time to “gas” the tank up…… 

Your filter will be working hard transforming toxic wastes (i.e. fish poo and uneaten food) into less toxic nutrients that can be removed from the system by mechanical means such as protein skimming or dilution via water changes. Now, a quick lesson in the biological filtration process.

Aerobic bacteria attack waste products and, therefore, produce ammonia from the proteins which are soluble and highly toxic. The nitrifying bacteria found in your filter, live rock etc., oxidize ammonia to nitrite (NO2) and then onto nitrate. These “good” bacteria colonise every available surface to undertake oxidization. The end result  nitrate (NO3) is far less toxic yet levels should be managed. In areas of anaerobic conditions (low oxygen), denitrifying bacteria occur. Nitrate is denitrified by facultative anaerobic bacteria that live in anaerobic zones (centre of live rock and bottom of sand bed) converting nitrate to nitrogen gas and nitrous oxide. This process is known as "denitrification" .

So, you put in your saltwater and switch on the pumps… The water starts circulating and nitrosomonas bacteria start to populate the filter (you may add bacteria in a bottle, get some from an established filter or add some live rock). They start oxidising ammonia to nitrite but don’t build up huge numbers until ammonia levels start to fall. (To grow and multiply they need a source of waste. A few hardy fish will get it all rolling.) Bacteria multiply by division so it takes time to build the army! For this reason, ammonia and nitrite levels climb slowly at first then plummet rapidly within a few days.

So after the bacteria are fully established, the ammonia and nitrites are consumed as soon as they are produced and the final nitrate compounds are then removed via protein skimming, denitrification and regular water changes.

So what does this all mean to me on my first day??

Understand that it takes time for these little critters to do their thing. Ammonia will peak at around 6-12 days post set up. Nitrites will build steadily until approximately day 22 – 30. Nitrates will continue to build up  until a water change dilutes their levels.

Below is a diagram representing  the ammonia to nitrate cycle in an average trickle or canister system.

So please don’t think you can add the water, look at the clear, clean water and think “yep, she’s apples! Let’s add all my fish and livestock so it is all pretty for the weekend when my mates are over for a BBQ!”…..  If you do, BEWARE!!!  By the weekend you will have a smelly rotten, pea soup mess littered with floating or dead fish!

PATIENCE is the biggest virtue in this hobby. Understand that you will need to cycle your tank for at least 4-5 weeks before you can add any substantial amount of livestock, and even then, at a gradual pace to allow the “army” to recruit new reserves.

Invest in a few test kits to monitor the cycle, and have salt water ready to do a few water changes along the way to dilute any toxins.

Use this time to read widely about systems, search the net for articles to help you and be informed before disaster strikes!

Talk to others with experience and ask the questions (even if you think they are dumb). It may save you a lot of heartache and dollars if you can avoid the pitfalls encountered by someone else.