The Nitrogen Cycle and You, or Who Said Anything About Learning Science?

I thought I left chemistry back in high school!

When you start a new aquarium, you’ll quickly learn that maintaining proper water chemistry is one of the most important aspects of fish-keeping. Now don’t worry, there’s only a few scary terms we’ll cover in today’s article, but knowing these things can mean the difference between a thriving mini-ecosystem and a tank full of sick and diseased fish. We’re going to look at water chemistry and fish waste products from a FW point-of-view, but the same basic information applies to SW as well.

Some New Terms (Here there be science!)

You’ve set up your aquarium. The gravel’s been rinsed and installed. The bubbling castle and the bubbling diver are bubbling and diving away. The plants (you used live plants, right? But that’s another article…) are gently waving in the current. The filter, lights, and heater are all working perfectly. It’s time to add fish, right? Not so fast! That spotless, pristine tank may look perfect, like the ones you’ve envied in the fish magazines, but right now it’s a sterile desert unable to support any life over the long-term.

Let me explain: Fish, when they eat, digest their food. That may seem pretty obvious at first, but the tricky part comes after digestion. Fish must expel the leftovers from digestion, and that waste goes right into the water they’re swimming in. A major component of fish waste, which can be excreted through the bowels or from the gills, is ammonia. Ammonia, at any concentration, is extremely stressful to fish, and at even moderate levels can kill.

This may seem like a death knell to ever keeping fish in little glass boxes, but there’s a savior on the horizon! Bacteria called Nitrosomonas begin the nitrification process by literally eating the ammonia, and converting it to nitrite. Nitrite isn’t much better for fish, so we need another superhero to come help. By the way, you just learned the first half of the Nitrogen Cycle! Nitrosomonas bacteria break down ammonia to form nitrite. See how easy that was? The second half is just as easy: Nitrobacter bacteria take the nitrite and convert it to nitrate. Nitrate, in low concentration, is tolerable to fish, but should be removed through regular partial water changes (but that’s another article…). These bacteria live in the environment all around us, but don’t exist in large enough numbers in your new tank to adequately support any fish yet. You can add a source of ammonia to the tank to help Nitrosomonas bacteria grow, but we’ll get to that later.

New Tank Syndrome – and How to Keep it From Happening to You!

Understanding the Nitrogen Cycle is crucial to being a successful aquarist. Eager new tank owners unfamiliar with proper cycling will often rush to fill their new tanks with fish, only to see the tank cloud up milky white. Then, the new aquarist watches in agony as one fish after another goes belly-up. The aquarist cleans the tank out, scrubbing off all the decor in the process, and starts all over again. Once again, the tank clouds up and fish die. What’s going on?

The milky white cloudiness that the aquarist is observing is a bacterial bloom; the Nitrosomonas are trying to grow into the tank to eat up all the ammonia being produced by the fish. However, the high level of ammonia in the tank from all those new fish has often done its dirty work, stressing the fish to the point of death, long before the bloom even occurs. When the disappointed aquarist cleans out the entire tank to start over, he’s reset the entire cycle back to the beginning. This is the dreaded New Tank Syndrome (NTS). NTS can also happen if the tank is improperly cleaned during routine maintenance (which is also another article…).

How does one avoid NTS? Simply get yourself some fish food and a good, quality water test kit. A water test kit is one item of fish-keeping gear that you don’t want to skimp on, because mismeasuring water quality parameters can literally mean life or death for your aquatic charges. To start cycling your aquarium, put a couple flakes of fish food into the tank (with no fish, mind!) every day. You should begin to see the water cloud up a little after a week or so of feeding your empty tank, so start testing your water. When your ammonia levels have spiked (and yes, you should be recording your ammonia levels when you test your water. Those little Moleskine notebooks work wonderfully for this!) and then dropped to zero, watch your nitrite levels. When these too have spiked and dropped to zero, you’re ready to start adding fish! Cycling this way can take several weeks, but it is so much safer than just sticking a fish or two in the tank and letting them stress it out while the water chemistry changes wildly around them. Do your fish a favor, and take it slow!

Happy Fish-keeping!

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