Black spot algae: Black spot algae form small, black spots on plant leaves. The cause of black algae is unclear, but excess nutrients (nitrate) and light help its spread. Control is very difficult, the best means to take is to remove affected leaves.

Black Spot- Usually these spots are seen as the fish is healing from ammonia surges. The area that was burned will turn black and this is the healing sign. The spots should fade within about 2 weeks. Orange Goldfish will sometimes turn black on their back and sides. After about 7 days the patches disappear and the fish appears orange. This is known as "Melanophore Migration" and is usually caused by any type of chemical irritant or traumatic injury. Some very common causes: high level of ammonia, low pH, flukes, or ick. The black color will not show up until the irritant is removed and the skin begins to heal. However if there are snails in the tank or the fish are living in ponds you should read below.

These spots could be from the pigmented cysts that contain the larval stage of a trematode intestinal fluke. Symptoms: Small black or brown spots up to 2 mm (0.08 inches) across. These spots appear on the body and fins of the fish and sometimes on their mouth and eyes. Treatment: Modern anti-parasite treatments should kill the parasites. The spots once formed may remain on the fish.