How would the nitrite cycle harm my fish i want to have?

Just trying to get a handle on this reef-keeping every one.
We are wandering why the nitrite cycle is so important, I have read some on the need for filtration ton do this cycle thing, just wandering what it is all about?
We want to do this right at the first try.

Well maddy,fish drink an enormous amount of the water they swim in to repel the salt as it tries to enter them on an osmotic level,they have two organs to remove the salt from this drinking water and then pass the water to their flesh to keep out the salt they are swimming in.

Nitrite is quite toxic and if it is in the water when they drink, which is constantly, it enters their system and will poison them very quickly, nitrate is a slow poison as it will create a domino affect to the fishes digestive organs and all will eventually shut down and the fish will still eat but is unable to digest these foods,just like drug caught fish, in fact heaps of fish that die this way have been thought to die of being drug caught.

Protein which is mostly pee,is not a big concern to fish as they recycle their urine with in mostly any way.

Maddy I'm reasonably new to this too and it all seems very confusing at first. A site that i have found very helpful is about.com

The basics as i understand it is that any organic matter which breaks down in an aquarium creates ammonia, this is then converted to nitrite and then nitrate which reacts with oxygen and leaves the tank. This process is facilitated by bacteria that are added to the aquarium when it is initially set up. To begin with either a few hardy fish or organic matter is added also to produce the initial ammonia. The ammonia and nitrite produced will be particularly high as the bacteria population needs to grow before it can cope with the elevated levels. Once ammonia, nitrite and nitrate have risen and then fallen back to acceptable levels the aquarium can be said to have been cycled. At this stage you can slowly add live stock hopefully without harming them since ammonia, nitrite and nitrate are all toxic above certain concentrations. Unfortunately it isn't easy and there are many different options and opinions about how to set up and maintain a marine tank which I am yet to fully understand. I hope this answers your question, I just thought I'd give my input as someone who is new to the hobby and in a similar position. My one piece of advice is read a lot and don't take anything you read or hear as fact until you have researched it thoroughly, except for on here of course!! The club members know what they are talking about and have a lot of years experience.

The nitrogen cycle is all about fish swimming in their own pee. As you can imagine, swimming in pee can’t be healthy. The main reason it’s so bad for fish is that unlike mammals which create urea, fish create pure ammonia. Ammonia is created when an animal breaks down proteins, either from old degraded protein it doesn’t need anymore, or from having a diet that contains more protein than it needs. Mammals turn ammonia into urea which is less toxic than ammonia and can be stored in high concentrations inside the body (bladder). But, because fish live in water, they have no need to store pee, they can pretty much just let it leach out of their gills and/or urinary tract. But, when a fish is contained in a box, the ammonia can build up and ammonia is very toxic. If you’ve ever smelled a bottle of cleaning ammonia, you can see why you wouldn’t want this on your very sensitive gills in high concentrations.

Ammonia kills a fish by irritating, burning and ultimately causing the gill tissue to clump together, which leads to suffocation.

But, luckily, there is an easy solution to this problem, bacteria! Certain bacteria love ammonia (because of the nitrogen content in it) and will gobble it up and turn it into nitrite (not to be confused with nitrate, spelled with an “a”). Normally, nitrite (with an “I”) is very toxic because it enters a fish’s bloodstream through the gills and reacts with the hemoglobin on the red blood cells. The nitrite turns it into methemoglobin which makes it incapable of carrying oxygen. Blood that can’t carry oxygen is useless and the fish “suffocates” from the inside out. In fact, humans can suffer the same exact fate if they drink water with high levels of nitrite in it, the condition is known as methemoglobanemia or more commonly blue baby syndrome. Nitrite, is actually much more toxic than ammonia, except………

In salt water! The chloride ions (Cl-) as in sodium chloride, the main ingredient in sea water actually work to block a fish from absorbing nitrite across its gills. Because seawater contains so much chloride, nitrite is actually of very little consequence to a fish. But in freshwater, it’s of major consequence!

One thing about nitrite though, is that bacteria also love it! Certain bacteria (different species than the first) will once again gobble up nitrite and turn it into nitrate. Nitrate is the least toxic nitrogenous waste compound. However, one thing about saltwater fish, is they drink constantly. The saltwater dehydrates them very quickly and they must drink, drink, drink to get that water back. The problem is that they will consume whatever is in the water which is where nitrate can become problematic. If there is a large amount of nitrate in the water, the fish’s gut will actually convert some of it back into nitrite, the toxic blood one. Mind you, they convert a very small quantity of it back into nitrite, so it takes a God-awful amount of nitrate to actually kill the fish, but nonetheless, it can still cause health problems if exposure is long term.

Nitrate is harder to get rid of than either ammonia or nitrite because very few bacteria like to use it. The exception is anaerobic bacteria (bacteria that cannot survive in oxygen) and plants, both of these organisms will gladly consume nitrate (which is why algae will thrive in high nitrate water). The plants will turn it ultimately back into protein (mainly enzymes) and the anaerobic bacteria will turn it into nitrogen gas (the main component of our atmosphere). The third option is to perform water changes to physically remove the nitrate from your aquarium.

The moral is, bacteria are good, actually essential to a healthy aquarium. Sterile aquariums are dangerous for fish even though it seems counter-intuitive. Personally, I never sterilize anything from my aquariums unless I have a very specific reason to do so, even rinsing filter material under chlorinated tap water can kill bacteria and create a little spike of ammonia in your aquarium. Nitrifying bacteria are growing on every single wet surface and so every part of the aquarium from the glass to the rocks to the filter is helping to detoxify the water from nitrogenous waste.

Cycling a tank is basically getting your bacteria population established prior to introducing fish. Some people use fish food or raw seafood (high protein content) which breaks down into ammonia, or the chemicals ammonium chloride or dilute ammonium hydroxide (cleaning ammonia). This gives the bacteria something to eat. The next part of course is you need bacteria. It is easily introduced from a fellow aquarist, a piece of liverock from the store or a rock you grab from the ocean. You can also buy commercial preparations of nitrifying bacteria in a bottle.

Sorry that was so wordy, I get all giddy about the chemistry stuff….

Thanks guys,lots of very helpful tips here.