It is fair to say that water quality is one of the most important aspects of fishkeeping. As all fishkeepers know (or should know), poor water quality is almost always the cause of ill health in fish. Simply put, the better the water quality, the more likely you are to have healthy, happy fish.
A fish tank is a completely closed environment; any waste produced by your fish, live plants or decomposing uneaten food stays inside the fish tank. This waste releases toxins into the water, such as harmful ammonia and nitrite. Usually, the biological filter will convert these toxins into nitrate, which is less harmful to your fish, but which should still be diluted through regular water changes.
However, if the filter stops working, you miss a water change or you’ve been overfeeding your fish, these toxins can build up, causing serious illness or even death.
Poor water quality causes fish to become very stressed, which weakens their immune system making them more susceptible to infections.
In a fish tank with good quality water and healthy fish, they should be able to fight off low-level infections without assistance, even if they have damaged their skin, slime coat or fins (which can be quite common).
However, if the water quality is poor, a fish with skin or fin damage is at greater risk of infection.
If you discover that your fish tank has poor water quality, then you should:
The key to maintaining good water quality is regular maintenance and testing.
You should check the filter is working and isn’t clogged up, clean the filter sponges (using water from your tank) on a regular basis and change them when necessary, conduct regular water changes, don’t overfeed your fish and, of course, test the water regularly.
Check out How to maintain good water quality in your fish tank for a more detailed guide.