Tropical water chemistry

Tropical water chemistry can be quite an in-depth subject but here we will try to cover the basics, this will include the nitrogen cycle in its basic form. Ammonia, nitrite, nitrate and phosphates, where they come from, what they do and how to prevent or remove them from the aquaria.
So firstly we have set up our aquarium, we have our box full of water, we have the heater in and the tank is up to temperature and now we want to add fish, so why can't we just put fish in the tank? The reason is that the water which comes from the taps in our homes is made fit for human consumption, and not necessarily fit for fish to live in. This is done by means of adding various chemicals, such as chlorine or chloramines, fluorides, fluoramines and a lot of other nasties, a typical list can be found on your local authority website. 

So the water has to be prepared by removing these contaminants, and so we add a water conditioner. This removes these elements and make the water safe for fish to live in. Another method of purifying the water is to filter the water through a reverse osmosis machine, and then add back in the elements we desire.
Once we have added the water conditioner, we must then consider fish waste and the consequences, and how to combat the effects.

Fish waste takes many forms; waste foods, excrement, urine, and even Ammonia passed back through the gills, this waste then ultimately breaks down into Ammonia, this is extremely poisonous to fish and can kill them at very low concentrations, luckily a naturally occurring form of bacteria called Nitrosomonas which consumes Ammonia and coverts this into a less, but still very toxic Nitrite, this again unfortunately kills fish, however, a second bacteria called Nitrobacter converts Nitrite into safe and more manageable Nitrate. So we need to ensure that the water in which we are about to put our fishes contains sufficient bacterias to cope with the initial Ammonia and convert ultimately to Nitrate. So how do we get these bacteria in the aquarium? In the past, it was common practice to "feed" the tank, which involved putting some biodegradable material such as fish food into the tank, and wait for this to break down, testing and waiting for Ammonia to spike, then Nitrite, and Nitrate, this is no longer the case as these bacteria are now available in suspension, in a bottle, this means that the fishes can be added on "day one" and monitored by use of a test kit.

In addition to the release of Ammonia, phosphate is also a by product from the waste production. Phosphorus is added to the tank by foods, which then is converted into Phosphates. Phosphates, Nitrates, and the presence of light can promote algae growth and so therefore we need to keep these to a minimum. This is generally managed by water changes although there are commercially available methods to reduce these "nutrients", however these should not be used as a substitute for good husbandry.