If your fish could talk, they would probably complain about one thing first — the water.
Most aquarium problems don’t start with the fish. They start with what is happening inside the tank that we cannot see. You might have the best filter, expensive food and a beautiful aquarium, but if your water quality is poor, your fish will struggle.
After years of maintaining aquariums across Melbourne, I can tell you this: you don’t need to become a scientist to keep fish healthy. You just need to understand the basics.
pH – Is Your Water Acidic or Alkaline?
pH tells us how acidic or alkaline your aquarium water is. Below 7 is acidic, 7 is neutral, and above 7 is alkaline. Different fish prefer different pH levels — African Cichlids usually enjoy harder, more alkaline water, while many South American fish prefer softer, more acidic conditions.
The biggest mistake I see is people constantly trying to adjust their pH. Fish don’t need “perfect” water. They need stable water. A stable pH that is slightly outside the ideal range is usually much better than constantly changing it.
GH – The Minerals Your Fish Need
GH (General Hardness) measures minerals like calcium and magnesium in your water. These minerals help with fish growth, strong bones and scales, breeding, and overall health. Hard water fish need more minerals, while soft water fish prefer less. The key is choosing fish that suit your water rather than constantly fighting your natural water conditions.
KH – Your Water’s Safety Buffer
KH (Carbonate Hardness) is what helps keep your pH stable. Think of it like a shock absorber for your aquarium. Low KH can cause sudden pH drops, which can stress fish and affect your beneficial bacteria. A stable aquarium is a healthy aquarium.
Ammonia – The Number You Never Want to See
Ammonia is extremely dangerous for fish. It comes from fish waste, uneaten food, dead plants or fish, and organic waste. In a healthy aquarium, ammonia should always be 0 ppm.
If ammonia appears, don’t just add chemicals and hope for the best — find the cause. Usually it’s because too many fish were added too quickly, the aquarium isn’t fully cycled, the filter was cleaned incorrectly, or there’s too much waste building up.
Nitrite – Another Warning Sign
Nitrite is produced during the aquarium cycling process when bacteria break down ammonia. Like ammonia, nitrite should always be 0 ppm. If you have nitrite readings, your aquarium’s biological filtration is struggling — this is common in new tanks or after adding too many fish at once.
Nitrate – The One You Manage
Nitrate is the final stage of the nitrogen cycle. Unlike ammonia and nitrite, small amounts of nitrate are normal. However, high nitrate over time can cause stressed fish, algae problems, poor growth, and increased disease risk. Regular maintenance, correct feeding and good filtration are the best ways to control nitrate.
Do You Need to Test Your Aquarium Every Day?
No. Testing is important, especially when setting up a new aquarium, but don’t become obsessed with chasing numbers. Your fish will often tell you something is wrong — hiding more than normal, not eating, losing colour, gasping at the surface, or acting differently. Learning to observe your fish is just as important as testing your water.
The Biggest Mistake Fish Keepers Make
The biggest mistake I see is people making too many changes at once. They see a number they don’t like and immediately add chemicals, change water, clean filters and move everything around. The aquarium goes from slightly imperfect to completely unstable. Stable water beats perfect water every time.
Keeping healthy fish doesn’t need to be complicated. Good filtration, sensible stocking, regular maintenance and understanding your water will take you a long way. If you’re in Melbourne, Aquatics by Ash can help with aquarium maintenance, water testing, aquarium setups and troubleshooting — healthy fish, clear water, a stress-free aquarium.