Why is Your Tropical Fish (Betta, Goldfish) Turning Black
By Eddie Waithaka @aquariawise
Fish turn black when there is a high amount of ammonia in the water. If you notice the color change on yours (beginning from the fins), perform a test and a do 50 percent water change and add prime conditioner in the tank if your ammonia readings are above 0.25 ppm. You can also give your fish a salt bath and treat your aquarium with Seachem stress guard.
Note that the black spots on your fish will be more apparent when ammonia burns on fish are healing. Fresh burns are colored pink and red before they turn black.
Horeover, the burns turning black does not mean your ammonia levels are down. Your fish could still be burning in places that are not yet black in color.
That said…
If the test you’ve done is negative- your water is pristine, with zero ammonia and nitrites- perhaps it is a natural color change common in fish like goldfish and betta. Goldfish can change color several times in their lifetime. They can transition from full black to red-orange all within 2 or 3 years.
Goldfish Turning Black from Orange
Goldfish turning black from orange or white (and vice versa) is a natural color change. The black shade could only develop into splotches that might fade out and reappear over time, but they can also be large permanent spots covering a significant part of your fish.
However, black spots on goldfish could also be ammonia burns.
Goldfish are dirty fish. They produce plenty of poop (high bioload) and waste a lot of food, which can cause poor water quality and ammonia spikes, especially in tiny or overcrowded tanks and limited filtration.
To ensure that the black spots developing on your goldfish are a natural color change and not ammonia burns, do regular water tests to check the ammonia and nitrites levels.
Another easy way to tell ammonia burns from a natural goldfish color change is the black spots will be blotchy and not form any pattern.
If you look at a goldfish changing color naturally, the shades are uniform, like a panda turning white and red, or the marks are repetitive on each scale, like a moor turning orange starting from the tummy— Ban Hammer; Reddit.
It is also less likely that your goldfish will develop black colors naturally as they mature unless it is a calico.
Why is My Betta Turning Black
Betta fish start out mostly cellophane, and most eventually develop their natural shades, including black spots and patches (marbling), depending on their ancestry.
Betta fish, like goldfish, can turn color as they mature.
Marble betta could turn black at a certain age, and you can expect more and deeper colors as they approach maturity. However, your betta should not only turn black. It should develop all of its natural shades at the same rate.
Plus fully grown mature betta fish do not change colors. It happens more in juveniles
If your betta is only turning black, you may want to test your water for ammonia and nitrites.
Even so, the rate at which betta fish gain colors, including black shades, differs in each fish and could depend on the environment. Colors on healthy betta fish in a safe, clean environment develop and intensify faster.
Do Fish Turn Black When Sick
Fish do not turn black when sick, but they can develop black spots on the skin and fins from parasitic flatworms. The infection does cause damage to your fish apart from the unsightly appearance.
The disease only appears on your fish as black spots but not splotches on fins and skin like healing ammonia burns or natural color changes on goldfish and betta.
Do Fish Turn Black When Stressed
A stressed goldfish is more likely to have faded colors, including pale blacks on calico and moor goldfish, but they won’t develop fresh black splotches just because they are stressed.
Black marks from ammonia burns could appear when your fish is healing, but when the lesions are fresh and stressing your fish, they are often red and pink (not black).
So, no…
Stressed fish do not turn black. They can get marking from ammonia burns, and the toxins in the water can cause them stress, but the black color does not indicate strain in your fish.
