Straight away I just want to say do not be disheartened if you have made any of these mistakes, everyone in the fishkeeping hobby has at one point in time made mistakes. The main thing is that we learn from them! I wish you the best of luck with your aquarium fish!
This is a common mistake, probably the mistake I see most often! This is when you have too many fish in your aquarium or fish which grow too large. This usually doesn’t end well and will lead to sick fish. Having too many fish in your tank causes water quality problems which itself can be dangerous for your fish but can also bring out disease. Again, with large fish in a small tank this stunts their growth causing them to have an early death. Solution: Always research the adult size of your fish and check what tank size is suitable. Never add too many fish to your aquarium, always test your water for ammonia, nitrite and nitrate.
Overfeeding can lead to poor water quality causing fish illness. This can cause a build up of waste in the water and if not quickly dealt with can impact the health of your fish. Solution: Feed as much as they will eat within a few minutes. Do not leave flake food in the tank if you have overfed, net it out to stop it impacting your water quality.
Too many fish too fast:
This is a common beginner mistake. If fish are added too quickly to an aquarium before it has been cycled, then toxic ammonia and nitrite will build up fast and it could be lethal to your fish. Solution: Cycle your aquarium before you add fish or add mature filter media from an established aquarium to your new one, this will introduce lots of beneficial bacteria. Research the nitrogen cycle before getting fish.
cleaning your filter under the tap:
Cleaning your filter media under the tap will kill your beneficial bacteria as tap water contains chlorine. This will cause a tank crash and could completely restart your cycle leading to serious water quality issues. Solution: Always clean your filter media in old tank water after a water change, this ensures there is no chlorine in the water and will keep your filter bacteria alive.
Fish species have different temperaments, some like to live in a school, and some can be aggressive. This can lead to fish killing each other, eating each other or injuries. Overall, this leads to a stressful aquarium which will be very detrimental to the fish. Solution: Always research the fish species you plan to add and check if they are compatible with each other. Do not try to push the limits as they are there for a reason, lots of newcomers think they will be the exception to the rule which sadly is not the case.