As an aquarist, keeping the health of my fish is my top priority.
It is important to keep in mind that in most cases, goldfish (or any fish for that matter) do not normally turn black.
It is usually a sign that the parameters of the aquarium water is or has been damaging in the past, and needs to be fixed.
Understanding how to resolve and prevent black spot problems and solutions is principal to the goldfish keeper.
Why Would a Goldfish Turn Black?
Several factors could be contributing to goldfish turning black, including genetics, disease or parasites, and water quality. Monitoring your goldfish’s behavior and body for lethargy, parasites, and discolorations can help you get to the source of why your goldfish is turning black.
Environmental factors such as too small a tank or infrequent water changes can quickly cause discolorations in goldfish.
If you suspect your goldfish has been harmed in some way, this could also have contributed to goldfish turning black.
To start, gauge your goldfish’s current environmental situation and think of any recent changes that have been made or inherent dangers in your aquarium (such as sharp edges).
1. Naturally Occurring Genetics
The goldfish is naturally undergoing color changes due to its genetics, which is usually unlikely.
If your goldfish is from a bad home or was rescued under questionable conditions, they could have lost their color due to stress and are not regaining it with their strength.
Even if you got your goldfish from a fair or carnival, these conditions are stressful and could result in loss of color until a proper environment is restored for them.
If you notice your goldfish losing color, this is cause for concern as it usually indicates excessive stress in the goldfish.
This could be due to a lack of proper husbandries, such as too little water changes.
2. Black Spot Disease
The second, and even more unlikely, reason for goldfish turning black involves a disease called “black spot disease.”
Black spot disease seems to be the most apparent cause because of how goldfish can turn black in spots or patches, but there are a couple of things that black spot disease usually requires.
Black spot disease is an immune response by the goldfish that is set off by other existing life in the aquarium, mainly snails.
With this comes the release of parasites, and is more common in outdoor pond environments.
3. Water Parameter Spikes
The most likely reason, due to unstable or extremely unfavorable water parameters.
Water parameters concern pH, high range pH, ammonia, nitrites, and nitrates. These, including temperature, should all be within certain ranges in order for your goldfish to thrive.
When these parameters damage your goldfish physically, the goldfish’s immune system compensates while it heals by turning that area black.
Out of all of these, ammonia burns are the most likely culprit for black smudge spots in goldfish.
What Causes Ammonia Burns?
Ammonia is a natural chemical byproduct of processes such as they breathe, eat and excrete.
While it is naturally occurring, excessive amounts of ammonia have the potential to have lasting and permanent health effects on your goldfish, and it is best if it is avoided.
When ammonia builds up to a toxic level, it “burns” the goldfish’s eyes, fins, gills, and skin.
When setting up a new tank, it is important to get a proper cycle (which can often take up to a month to achieve) going so that you do not cause “new tank syndrome”.
Because the water is not cycled correctly, ammonia accumulates faster to toxic levels.
Additionally, the water in the bag from the pet store may have accumulated excessive amounts of ammonia and should not be added to the existing cycle.
If your goldfish is in a tank or bowl without a filter, ammonia will undoubtedly be a problem without major and frequent water changes, which can be stressful to goldfish.
The smaller the enclosure, the more likely ammonia is to build up to a deadly level and damage your goldfish’s health.
When this happens, goldfish do not initially give off any physical signs other than being lethargic.
When goldfish begin to heal from ammonia burns, their scales turn black as a response to healing.
Solutions for Goldfish Turning Black
1. Frequent Water Changes
If you are here before getting a goldfish, even better! You have the chance to learn about goldfish husbandry in advance and understand their needs in captivity.
Goldfish, especially large breeds, need large aquariums or ponds. This is because goldfish have a large bioload, meaning they are messier than your typical fish so they need more cleaning up after.
When feeding your goldfish, start off with the smallest amount possible and wait until they finish that batch before giving a little more. This can help prevent overfeeding and therefore avoid ammonia spikes.
Uneaten food can get stuck under decorations and eventually decay, which can cause water parameters to go off of the charts.
Weekly water changes that include taking out or moving decorations is recommended to loosen any hidden debris.
2. A Larger Aquarium or Filter.
If your goldfish is in a bowl or tank that is less than twenty gallons, it may be time to upgrade their enclosure for their sake.
Small bowls often cannot have filters, or the current is too strong in small tanks.
By upgrading their enclosure, you add more water and therefore lessen the number of times you have to do water changes.
This will also give your goldfish more room to move around and likely make them happier and healthier.
The Penn Plaxx Cascade 1500 is a good option for those with a lot of goldfish as it handles up to 200 gallons.
3. Test your Water.
Stress, sick, or agitated fish will give off more ammonia than usual, so it is important to pay attention to any irregular behaviors.
Giving your goldfish more hides, driftwoods, plants, and less time with lights might help with stress levels.
A quick and sure way to get to the root of your goldfish’s problem is to test the water parameters,
which may be the most important part of maintaining your goldfish’s health.
Water parameter kits come in liquid and strip form, with the liquid being more accurate and the strip being more convenient.
These regular tests will let you know what parameters (pH, nitrites, nitrates, temperature, etc.) your water quality is actually at,
and then you can work to tailor them to your goldfish through husbandry changes.
4. No Snails
Even though black spot disease is rare, it is not recommended to get snails to cohabitate with goldfish.
This is because snails can transmit other diseases, not only black spot disease, and also reproduce at a massive rate when fully mature.
In the case of pond snails, the most common and prolific type of snails, they can multiply at alarming rates and soon infest your tank.
If you really want to get a snail, it is recommended to get a quarantine tank in which they live for one to three months.
If they show no signs of underlying health conditions, it can be safe to add them in with your goldfish while taking all necessary precautions.
Will My Goldfish Ever Turn Back to its Normal Color?
The good news is that with proper aquarium husbandry goldfish can turn back to its normal color, and will recover from ammonia burns!
You first have to identify the source of the problem as outlined above, and then correct your husbandry as you see fit.
Another option is to consult your local fish store, who may be able to help you in regards to getting a proper cycle in your aquarium.
If you are seriously concerned for the health and safety of your fish and have no access to a water parameter kit,
Amazon offers a free service in which they test your water parameters for free if you bring a sample to a location near you.