The type and amount of filter necessary depends on the nature of the individual aquarium. A function of bacterial population size is biological efficiency, and that is in turn dependent on the available colonisable area and oxygen supply. When you are choosing a filtration system you need top consider tank size, metabolic loading, and water movement. This will determine what filter type capacity and turnover rate will be perfect for your specific circumstances. You can get expert advice from your retailer. Filter efficiency can be monitored using the kits for measuring water quality.
Although filtration of a biological nature will handle nitrites and ammonia, it will not take care of nitrates. If you don’t do something else it will build up gradually, and while they are basically harmless long term exposure can shorten the lifespan of some fish. Sudden exposure to high nitrate levels is usually fatal for most new fish.
The best way to reduce nitrates is to replace part of the water in the aquarium routinely. How much and often depends on the tank, but twenty to forty percent weekly is a good starting rate . This rate should be a guide only. In order to determine how often and how much water to swap out, you need a testing kit and test your water regularly to get a picture of how fast your water is become toxic. If you have a high ratio of fish/plants to your tank size…. you are going to need to change the water more frequently. The constant yo yoing of water quality will likely also effect the health of your fish in any case so always have the biggest possible tank with the least possible number of fish if you are looking for good survival rates.
Re test regularly but especially when you make changes. Addition of new fish and or new plants is going to greatly increase the speed in which problems arise because of the extra nutrients going into the water from the digestion of food, and rotting of plant material. (Editor- my cichlids love plants, but destroy them fast. As a result when i have plants in with cichlids I need to do more frequent water changes and feed the cichlids less food).
Be aware that tap water as well as containing chlorine may contain nitrates and nitrites depending on where you are located. Letting water site will allow the chlorine to evaporate, but this will not remove the nitrates/nitrates. Be sure to test your tap water as well as your tank water for problems.
You can monitor with a test kit to determine whether the routine should be modified. The most common water amount to change at any one time is 25%. This amount seems to provide the best combination of improved water quality from reduced nitrate/nitrite levels with low levels of risk of shocking the fish from the sudden change in the water makeup. Some experienced fish owners, who “know” their fish may opt for large or smaller water changes at a time.
Replacement water should be cleaned of toxins and be of the right temperature and chemistry. Fresh water is preferable even though chemical media are available for removing nitrates, because it has the added feature of stimulating fish and replenishing minerals used up by the fish. Topping up to replace water lost by evaporation is not enough for a partial water change; you need to replace water for more often than it will ever evaporate and in much larger quantities.