When starting a home aquarium, what you want to achieve is a balanced eco system within the aquarium and this does take time to achieve. Rushing this with the excitement of starting a new aquarium generally leads to disappointment and the mortality of fish. Being patient and allowing your aquarium/eco system to be created and develop is the key to enjoying your aquarium and you will have less problems.
Where does the Ammonia come from?
Fish will create waste in various ways including feeding as well as any uneaten food/protein and this waste will decay into ammonia as well as will other organics in the Aquarium. Ammonia is toxic to fish and high levels of Ammonia will affect the gills and rupturing blood circulating and can be seen in redness around fins and clamping of fins and is a painful death. Ideally you want zero or very low levels of Ammonia in your tank. An Ammonia test kit will help you identify the levels of Ammonia in your aquarium.
In a balanced established tank, bacteria will convert the toxic Ammonia into a less toxic form being Nitrite, the bacteria uses the ammonia as a food source. In a new tank there is no established bacteria to do this and the ammonia builds up to a point where the toxicity causes the mortality of your new fish.
Bacteria Farming -
The building of bacteria does take time and there are a few ways that you can help this process. You can purchase items like Quickstart which help with establishing bacteria where QuickStart has the bacteria in a dorment state in the bottle and activates when added to the aquarium to help start up. Another way is adding seeded media - seeded media is media that is already colonised with established bacteria and will generally come from an aquarium that already has a balanced eco system. Keep in mind that although getting seeded media is a good and helpful way of giving your aquarium a good head start it does have its drawbacks, mainly if the tank that it is coming from has issues with disease, pathogens or even snails this can be transferred to your new home aquarium and you will have to deal with the same issues. there are also methods being a fishless cycle and also a fish cycle and will go into this further below.
When we say balanced we mean that there is sufficient bacteria to deal with the waste/ammonia produced and in the early stages a new tank is limited and time is needed for the bacteria to colonise, reproduce and build to a level where it can handle the waste.
Too Many Fish Too Soon -
Resist the temptation of buying all the fish you want for the tank in one purchase as this will inevitably throw you aquarium out of balance where the bacteria will not be at the required level to handle the mass increase of Ammonia. Start with one or two small fish and give the bacteria ample time to populate to handle the increase of ammonia and when that is complete buy a few more and continue this process until you have all the fish that you want for your aquarium. It is a slower process but you will find it more rewarding and you will not have the disappointment of dead and dying fish.
In the above we have spoken about Ammonia which is highly toxic to fish in high levels and the bacteria that will consume this are called Nitrosomonas - the result of this bacteria consuming the Ammonia is then still in a toxic form but less toxic than that of Ammonia and that is Nitrite and similarly this is also consumed by bacteria (Nitrospira) with the last stage being Nitrate the safest point for fish. This conversion of Ammonia to Nitrite to Nitrate is the Nitrification Process. As more and more Ammonia converts to Nitrite and Nitrite to Nitrate the end result is that the levels of Nitrate will build up and this is where changing the water will reduce the build up and the more often you change the water the less Nitrate in the water - the less Nitrate in the water, the better the conditions and the better the growth of your fish.
When a aquarium can do this it is balanced and also called cycled. The time that it takes to do this varies with the different techniques used to cycle an aquarium and also the temperature with 25-30 degrees being optimum temperature range for bacterial growth.
Four different ways to cycle your tank.
Fish Cycling: Fish cycling is generally using a hardy type of fish and feeding and the waste from that fish to generate/colonise bacteria in the Aquarium - The down side of this is that the fish used is generally not one that you want in your aquarium when the cycle is complete and the fish does undergo the increases of Ammonia toxicity and Nitrite toxicity.
Fishless Cycling: Fishless cycling is adding ammonia either in a pure ammonia level or even just adding a ammonia source which can include adding fish food with out fish in the tank and this will decay into Ammonia and some also suggest adding a prawn head again where it will decay and create Ammonia.
Bacteria in a Bottle: Bacteria in a bottle is as we mentioned above and using products like API QuickStart, Fluval Cycle to add bacteria into the aquarium by dosing the required amount and with QuickStart, Fluval Cycle the bacteria is activated when added to the aquarium.
Using Seeded Media: Where filter media is used from a aquarium that has a established cycle and the bacteria on the filter media is then transferred to the new home aquarium to colonise - as mentioned earlier - what ever issues are in the tank that the filter media is taken from can be transferred to your new tank too.