Every aquarium should have water changes performed; it is a vital part of the hobby. Fish in water produce ammonia, this ammonia is toxic to them, it can burn their gills and be fatal if levels rise high enough. Luckily in a cycled aquarium the bacterium inside the filter converts this ammonia into nitrite, which is still harmful, but nitrite then gets converted into nitrate. Nitrate is far less dangerous to fish and can be tolerated long term at low levels, although it is best to keep this nitrate levels as low as possible, around zero if you can for good fish health. Over a period of a week or two, nitrate levels in an aquarium will begin to rise until they become too high. To keep your fish happy and thriving, we recommend a water change at least every few weeks to ensure nitrate levels remain low.
Pro tip: If you need to clean out your filter sponge do it when you do a water change, rinse the sponge in a bucket of old tank water. Washing your filter sponges under the tap can kill off your beneficial bacteria as tap water is not dechlorinated. Always remember to add tap water conditioner to new tap water before you add it to your aquarium this neutralises the chlorine.
It is worth noting there are many other benefits to carrying out water changes. If you have plants, doing a water change will help to replace micronutrients which the plant will use to grow. The same concept applies to replacing elements used by coral in a saltwater aquarium. Keeping your nitrates low can help reduce the amount of algae growth you have in your aquarium. Carrying out water changes also has the added side benefit that whilst spending time around your aquarium you will be far more likely to notice any changes or issues and you can act on them sooner rather than later.