Fish Tank Maintenance 101

LAST UPDATED 21st of February 2023

This article is written by Pet Circle veterinarian, Dr Emilee Lay BSc (Vet) Hons BVSc and edited by Dr Nicole Wynne Bsc BVMS MANZCVS (Unusual Pets)

It’s a good idea to do regular water testing at home to ensure you’re not caught out by a sudden ammonia or nitrite spike. Being proactive can save a lot of heartache. Many fish diseases can be attributed to poor water quality. Although filters can reduce the maintenance of your tank, you still need to do regular water changes (at least once a week or more frequently for smaller tanks) to help keep your fish happy and healthy. You will need:

  • Water testing kit
  • A bucket or two 
  • Gravel siphon 
  • Biological filter chemicals/additives (Optional) 
  • Fish net 
  • Water conditioners

Understanding Your Water Test Results

Water testing identifies the levels of particular chemicals in the water that can affect water quality, and therefore fish health. There are several chemicals and other parameters that should be tested for including: Ammonia, pH, Nitrite, Nitrate, GH and KH.

These should be tested at least once a week, and prior to a water change. Water testing kits come as extensive kits with droppers all the way to simple strips. Using a combination of both can make tank maintenance long-term much easier. Dropper kits can be finicky but are more accurate. Dipstick strips are great for testing the water on the go. You can even have in-tank testers if you want to closely monitor ammonia and pH levels. 


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This is a measure of the acidity of the water or the number of hydrogen ions present. Higher levels of hydrogen ions indicate acidity, and lower levels indicate basic water. Most fish do best at around a pH of 7, or neutral, but some species of fish prefer acidic water. Buffers can be added to your tank to help create the ideal pH for your tank. If your pH is too high, you may need to do a partial water change. Repeat water tests until your pH has dropped into range. If it is still abnormal check your GH and KH levels. 

Some common pH ranges for fish include:

Goldfish 6.5 (minimum) -7.5 (ideal)

Community Tropical Fish - 6.8-7.8

Cichlids 7.8-8.5

Discus 6.0-7.0


This is a waste product produced by fish, a bit like how urine is produced by mammals. This is released by fish through their gills and vents and becomes harmful at higher concentrations. Excess ammonia causes illness by harming your fish’s natural defenses against infection, such as their slime coat and immune system. Higher levels can even cause organ damage and failure. Concentrations of ammonia should aim to be at 0.

Signs of high ammonia levels include: red, bleeding gills, abnormal body colour, gasping for air at the surface of the water, abnormal mucous production and death 

If you have high ammonia in your tank, immediately perform a water change of at least 25%. Additional chemicals can be added to rapidly convert ammonia into a non-toxic form. Filter additives can be used to also reduce ammonia levels. During an ammonia crisis, make sure to reduce feeds to help lower ammonia levels. Continue to carefully monitor your water parameters until the ammonia levels drop to 0. This may need retesting for several weeks.  



This is one of the most toxic pollutants that can be found in your tank water. These are formed as a result of bacteria breaking down ammonia. Concentrations of Nitrite should always aim to be at 0. 

High nitrites can result in abnormal behaviors from your fish including rapid gill movements, shimmying, and pale or dark colouration with brown discolouration to the gills. 

Reducing Nitrites involves large water changes and adding beneficial bacteria and aquarium salts to the tank. Ensure you increase aeration and reduce feeds whilst treating your tank. You will need to do water tests daily until the nitrite levels drop to acceptable levels. 


This is produced as part of the all-important nitrogen cycle in your tank. Toxic nitrites are converted into less harmful nitrates thanks to the beneficial bacteria in your tank. However high nitrates can still be dangerous to your fish if exposed over a period of time. High nitrates can indicate excessive waste in your tank. In planted tanks, nitrate levels being moderately high is normal, in order to help feed your plants. Excess nitrates can lead to algal blooms. Most fish can tolerate Nitrate levels up to 40ppm (mg/L). Marine fish however need low to zero nitrates. 

Unlike nitrites and ammonia, nitrate toxicity tends to be more a slow burn. Fish will appear flat, lethargic, have dull colours, and have a change in their appetite. 

High nitrates can be managed with water changes, adding aquarium plants to your tank (you can even use indoor plants and propagate them in water on top of your tank) as well as water additives to reduce nitrates. 

GH and KH 

General Hardness refers to the concentrations of calcium and magnesium dissolved in your tank water. Hard water refers to those high in calcium and magnesium and soft water is the opposite. KH or carbonate hardness measures the concentrations of carbonate and bicarbonate. These minerals can be present in your tap water and are influenced by your water source as well as any treatments done on your water. KH can help stabilize the pH in the aquarium i.e. high pH’s tend to have a high level of KH, and low pHs have low KH levels. 

Different fish thrive in different GH and KH levels. Partial water changes can be used to decrease KH and GH. Different buffers or using deionized water can also tweak GH and KH levels. 

How to Clean Your Tank

Prior to doing any water changes, wash your hands and arms to reduce contaminating your fish tank with any topicals, skin oils, or perfumes. Turn off any heaters and filters whilst cleaning. A minimum of 20% water change is recommended per clean. More drastic water changes i.e. 50-75% should be reserved for emergencies such as ammonia or nitrite spikes. Large-volume water changes can be quite stressful for fish. 

Cleaning Your Gravel


Gravel vacuums are perfect for siphoning up debris in the gravel and changing out the water. Vacuums with a pump can help speed up the siphoning process, otherwise, you will need to manually start the siphoning effect by vigorously shaking your vacuum in your tank.

Make sure to pick a gravel vacuum suitable for the depth of your aquarium. Remove decor and furniture to give them a gentle brush to clean any algae or scaling. You can leave your fish in your tank during a clean, but if you need to do a large change or deep clean you can place them in a temporary tub of their tank water with an air pump as you clean. 

Cleaning Your Filter


Make sure you have unplugged your filter from the power outlet before cleaning it. Put some tank water into a bucket. Filter media should only be cleaned with old tank water OR dechlorinated water. Do not use tap water as this will kill any beneficial bacteria in your filter, and you’ll have to cycle your tank again! Make sure to have plenty of towels on hand to clean up any spills.

Depending on your tank’s bioload, stocking rate, and the type of fish you have, you may only need to clean the filter once every couple months, or a minimum of once a month. If you need to replace any filter media make sure you do so gradually. Don’t forget the insides of the filter tubes, and use tube brushes to remove any algae or build up that can affect water flow through the filter.

Read more in our Complete Filter Guide. 

Cleaning Aquarium Glass


Don’t forget about your aquarium itself! Mineral deposits and algae can build up without proper maintenance. Use aquarium-specific glass/tank sponges to clean your aquarium.

Depending on whether your aquarium is glass (most common) or acrylic (less common) using the wrong sponge can cause scratches to the surface. Scratches not only are aesthetically unpleasing, but they can harbor pathogenic bacteria. Glass scrapers can also help to remove algae buildup on the glass. Magnetic leave-on cleaners are great for maintaining the clarity of your glass in between cleans. 

Adding Water To Your Aquarium


Before adding new water back into your tank, ensure you have added the appropriate water conditioner. Dose based on the TOTAL volume of your tank. Give the water conditioner at least 20-30 minutes to kick in before adding the water to your tank. You may also want to add in a Biological Cleaner as well.

Adding beneficial bacteria can help break down wastes and keep the cycle in your tank going. Most of these additives can be done with each water change. If you have a tropical tank, ensure the water is not significantly cooler than your tank water as the sudden temperature change can cause quite a shock to your fish. Gauge this with your tank thermometer. When pouring water into your tank, go slowly, to minimise stress on your fish. Use smaller jugs or a pump to refill your tank. 

Further Reading

Want to read more? Check out our other articles:

How to Cycle Your Fish Tank

A Guide to Fish Filters

A Complete Guide to Setting Up Your Fish Tank

Common Aquarium Problems and How to Solve Them

How To Feed Your Fish

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