Our Top 8 Common Fish Tank Problems and How to Fix Them

LAST UPDATED 17th of March 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)

Common things happen commonly and fish tanks are no exception to this saying. Many issues that occur when fish keeping can be related to poor water quality, an improperly cycled tank, and a lack of quarantine measures when introducing new fish. Successful fishkeeping involves setting up your tank with a bit of patience and implementing a routine when it comes to maintenance that will keep your tank flourishing for years to come.  Let’s go through our top 8 Common Fish Tank problems!

Problem #1 Poor Water Quality

Routine maintenance of your tank includes regular water changes and cleaning as well as closely monitoring your water quality. Aquariums are a closed ecosystem, and as such excessive wastes whether that be from overfeeding, overstocking, dead plant material, or fish poop and pee can rapidly build up and overwhelm the all-important Nitrogen Cycle. 

Remember that the Nitrogen cycle is responsible for breaking down toxic ammonia to nitrites to less toxic nitrates. A fully cycled and well-maintained tank will have 0 ammonia and nitrites with some nitrates. Your water quality is influenced not only by your tank maintenance but also by the type of fish you keep. Goldfish are notorious for polluting their tank water. Poor water quality can suppress your fish’s immune system and make them more susceptible to disease. 

The general rule of thumb to improve water quality are:

- Rigorous water testing

- Partial water changes (with larger volumes up to 50% reserved for ammonia spikes and nitrite spikes)

- Reducing biomass (by thoroughly cleaning gravel, and reducing the amount of food fed) 

- Checking your mechanical filter (Is it working? Is it blocked? Does it need to be cleaned?)

- Adding chemical filters to detoxify or correct the abnormal parameters 

- Adding in Beneficial Bacteria to support your biological filter 

Repeat this process until your water parameters improve. Depending on the severity of the chemical spike you may need to repeat this every couple of days or weekly until parameters return to normal. Most tanks require a minimum of once-a-week water changes and maintenance. Overstocked tanks and tanks with fish that are heavy polluters may need more frequent water changes. 

Check out our guides below on Cycling a Fish Tank and Fish Tank Maintenance for more information.

Problem #2 Help! My Tank Is Super Cloudy!

Have you set up your tank and woken up to find the water is very cloudy? This can be caused by improper cycling, bacterial blooms, poor filtration, overfeeding, and excess waste. Having a good mechanical and biological filter will go a long way to keep your water crystal clear. 

If you are in the midst of cycling your tank, cloudy water can be due to a bacterial bloom. This is not uncommon during the early stages of cycling. As the cycle progresses, this cloudiness should resolve. The best course of action is to do NOTHING! Cleaning out the filter or changing the water during this time will prolong the cloudiness. You can certainly add beneficial bacteria or live plants to your tank which can help boost the cycling process. Continue to monitor ammonia and nitrite levels during this time. 

If your tank is established but the water is cloudy then these bacterial blooms can be a result of poor water quality, or if you’ve overwhelmed or killed off your beneficial bacteria in your tank through over-cleaning, changing your filter media suddenly, or overstocking. Adding beneficial bacteria to support your tank is essential. If the bacterial bloom is from excess wastes or abnormal water parameters then partial water changes are a must. Removing debris from your tank such as fish poop, dead/decaying plants, and uneaten food can help improve your water clarity. 

Did you recently add gravel to your tank? Cloudy tank water can also be due to gravel that hasn't been thoroughly rinsed before adding to the tank. Make sure to rinse your gravel until the water turns clear before adding it in. If you’ve already added it in then you will need a gravel vacuum and fine wool in your filter to filter out the finer particles. Water clarifiers can help speed up the process. 

If your water is brown or yellow it may be from tannins leeching from your driftwood. You can leech your driftwood in a tub separate from your tank until the water turns clear. Boiling can also speed up the leeching process. Tannins are not dangerous to fish and can create an ideal environment for certain fish by creating a ‘Blackwater’ aquarium setup. 

Problem #3 My Tank is Full of Algae!

Although green plants in a tank can be pretty to look at, algal blooms are less appealing. Algae thrive in well-lit tanks, or tanks with a lot of exposure to sunlight. In addition excess wastes/nitrates in the water feed the algae resulting in huge booms - sometimes overnight. 

Remember when positioning your tank inside your home to be mindful of the amount of sunlight that may be coming into the room. Tanks should ideally be placed in a low to moderately-lit room, away from direct sunlight. Artificial lighting should be placed on a timer, with only 8-10 hours of light at best. If your tank is in a well-lit room, switch off your aquarium light during the day. 

Regular water changes, glass and filter cleaning, and cleaning any excess waste can help reduce the incidence of algal blooms. Use Algae scrapers to help clean your glass or any aquarium furnishings. Planted tanks are sometimes more prone to algal blooms due to the addition of artificial light and fertilizers needed to maintain their appearance. Take care to dose your tank accordingly when fertilizing. 

Asides from reducing light exposure, a UV steriliser can help eliminate algae in your tank, these can be found at specialty aquarium stores. Algae-removing chemicals are also available but they should only be used as a last resort. Consider them more as a bandage fix rather than a long-term solution.  Addressing the underlying causes of your algae issue will keep your water clearer in the long run. 

Problem #4 Help My Fish Have Suddenly Died!

Dead fish can be very upsetting, especially with the time and effort it takes to set up and maintain a tank. Despite a reputation for being a cheap pet, fish have quite a lot of character and with time can recognize you (or perhaps feeding time to be precise). Common causes of sudden fish death include ammonia, nitrite, and even nitrate spikes from poor water quality, inappropriate water parameters for the type of fish you own, poor oxygenation, and disease. 

Whenever there is a fish death, it's important to remove the fish from your tank as soon as possible. It may sound very repetitive, but the next step is to test your water. Are your pH, Ammonia, Nitrite, Nitrate, and temperature all within normal limits? Adjust your water parameters as needed with water changes and using biological and/or chemical filter additives. Observe your fish as well. Are their scales and fins intact? Are they gasping for air? Sitting at the bottom of your tank? Are they acting abnormally - swimming rapidly or floating at the top? Are your fish bullying each other? Have you been overfeeding them? Are their scales or gills red?

The key to success then it comes to fishkeeping is having a properly cycled tank, good tank maintenance practices, stocking your tank appropriately, and feeding them just enough! If you’ve identified water quality issues as being a problem, perform a partial water change and add in additional beneficial bacteria to help your tank get back up and running. If you have sudden or mass fish death, consider having an exotics vet assess your remaining fish. 

Problem #5 Help My Fish Have Dropsy!

If your fish are swimming abnormally, appear a bit swollen, with bulging scales or a pine cone-like appearance they may have “dropsy”.  Dropsy is a general term and can have lots of different causes. Dropsy is caused by fluid building up in the body cavity of the goldfish, and unfortunately, a common cause is organ failure. Other causes include bacterial infection, poor water quality, and parasite infection. Treatment is dependent on the cause and involved providing supportive care to your fish during that time. Don’t forget to test your water! 

If your fish is unwell, separating them into a smaller quarantine tank, that has an established/cycled filter, can help you medicate and manage them without harming your other fish or delicate tank ecosystem. If it is bacterial in nature, broad-spectrum antibiotics can be used to help manage them. Make sure to remove any carbon in your filter as this will affect the absorption of medications. Aquarium salts can be used to help improve and boost the immune system but are not the mainstay of treatment. 

Where possible have your fish assessed by an experienced aquatic vet. The Fish Vets are available in Australia Wide. Local exotic specialty clinics can also assist with treating your fish. Speak to our Friendly Vet Team for a list of clinics!

Problem #6 My Fish is Swimming Upside Down!


If you notice your fish are having difficulty swimming, are swimming on their back or side, sinking to the bottom of your tank, or are stuck floating to the top, they may have a Swim Bladder problem. The swim bladder is in charge of maintaining neutral buoyancy. Inflammation or diseases impacting the swim bladder can lead to swim problems. Many old wives' tales will mention feeding peas and adding aquarium salts to the water. Peas can help with swim bladder issues that are due to blocked swim bladder whilst adding aquarium salts can help boost their immunity. 

However it's important to realize that Swim Bladder issues can be related to bacterial infections, a suppressed immune system, structural/skeletal abnormalities, and most importantly poor water quality. Fancy goldfish such as Ranchus in particular are prone to swim bladder issues due to their abnormal anatomy. Goldfish inflate their swim bladders thanks to a special duct between their esophagus and swimbladder. As they inhale food at the tank's surface, they suck in a lot of air, which can lead to swim bladder issues. 

Once again check your water parameters! Separate your affected fish to avoid them being bullied by other tank mates or bumping into your tank furniture. If your swim bladder issues are caused by digestive problems then increase the temperature of your tank, and provide high-fibre foods such as cooked peas (this is applicable mainly to omnivorous or vegetarian fish). General broad-spectrum antibiotics can be used to help if there is an infection of the swim bladder. Depending on the cause Swim Bladder disease can be fatal. 

Where possible have your fish assessed by an experienced aquatic vet. The Fish Vets are available in Australia Wide. Local exotic specialty clinics can also assist with treating your fish. Speak to our Friendly Vet Team for a list of clinics!

Problem #7 My Fish Have White Spots on them!


Have you noticed that your fish appears to be covered in a fine white sand/salt-like substance? They may have White Spot, which is a contagious parasitic disease caused by Ichyophthrius multifilis or Ich. They have three stages to their lifecycle. These parasites multiply rapidly in your tank and then attach themselves to your fish feeding off their bodies. By the time you see these salt-like growths on your fish the parasite is fully developed and often well-protected from any medications. As they drop off your fish, they attach to the substrate, plants, or other surfaces - at this stage, they are susceptible to treatments added to your water. They then begin reproducing, in the search of a new host, during which time if no host is found they will die. 

Ich can be fatal, as each round of the cycle drastically increases the number of parasites in your tank and continues to weaken your fish, making them susceptible to secondary infection. Prevention of Ich involves maintaining water quality and quarantining new fish/plants before introducing them to an established tank. You can read more about how to set this up in our article 

Treatment involves, increasing the temperature in your aquarium, using a gravel vacuum to suck up any parasites in your substrate, and adding in White Spot Remedy or treatment from your local aquarium. Having a hospital tank can be beneficial during the treatment period. If your entire tank needs treatment, make sure to monitor water parameters carefully. 

Problem #8 Why Do My Fishes Fins Look Frayed? 


Have you noticed your beautiful fish's fins look a bit frayed or worse for wear? They might have fin rot! Fin rot is usually a sign of underlying health issues or poor water quality. It is caused by bacterial infections secondary to trauma (from other fish nipping or attacking the delicate fins) and stress (from poor water quality, overcrowding, or other diseases). Fins can appear frayed, fuzzy, milky, or even bloody. 

Fin rot can be prevented by, you guessed it - maintaining good water quality in your tank. This includes routine water changes, water testing, and minimizing overfeeding and overcrowding. Be mindful of the type of fish you keep together as some species can be more aggressive or territorial than others. If you have a particularly aggressive fish that is nipping or attacking other fish, consider separating them into another tank. For fancy goldfish breeds with elaborate tails and fins, take care with any sharp or jagged decorations as they can easily hurt themselves on them. 

To treat fin rot, separate your affected fish into a hospital tank. You can use water medications such as MELAFIX to help treat any bacterial infections. Make sure to remove the activated carbon in your filter whilst using this medication to ensure it is effective.  Aquarium salts can help to boost the immunity of your fish that are affected as well. Check your water parameters and change or correct any issues as needed.

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Further Reading

Want to read more? Check out our other articles:

How to Cycle Your Fish Tank

Fish Tank Maintenance 101

A Guide to Feeding Your Fish

A Complete Guide to Setting Up Your Fish Tank

Feeding Your Fish

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Please note that as our vets have not examined your pet, any advice given is general in nature. If you believe your pet is unwell, please seek direct veterinary attention.