Cause of this disease is decrease water pH below 5. This may happen rapidly (direct jump a few values) or for a longer time (pH jump is gradual). In the first case, the fish start to behave strangely and they signal worrying signs at once. In the second case, symptoms of the disease may be visible after longer time or only when we insert new fish to the aquarium or when we keep there old fish with weakened immune system. Other fish was able to adapt to new conditions in a measure. The most frequent symptoms of the disease are breathing problems. The reason for this is gradual degradation of the gills and direct impact pH on the saturation of hemoglobin with oxygen. pH reduction reduces binding oxygen from the water and its carrying together with blood. Reduction of degree saturation hemoglobin with oxygen is cause increase pressure of the carbon dioxide in the blood at the same time. Then carbon dioxide poisoning is the direct cause of possible fish deaths.
We need find and eliminate main cause of water pH reduction. Next we need check all water parameters in the aquarium: water pH, hardness, ammonia, nitrites, nitrates. Next we do about 1/3 partial water change without removal the fish. We need check water pH and other water parameters after each partial water change. We need also increase oxygen saturation of the water. Water for partial change should have neutral pH (pH=7). We should use adequate vitamin preparations and water treatment conditioners in order to strengthen fish immune system (e.g. Tetra AquaSafe, Sera Aquatan, JBL Atvitol, etc.). We may also basify water in the aquarium by insertion there lime decorative elements but we need do this cautiously. We should immediately commit an act of euthanasia for fish with damaged gills.