I have a freshwater aquarium in which one of my larger fish is getting cloudy eyes. Do you know what causes cloudy eyes in aquarium fish, and is there any way I can treat it?
Several things can cause cloudy eyes in aquarium fish. Internal parasites, such as protozoa or flukes, are one cause. Another is the onset of cataracts in fish. I’m not aware of any treatments for those problems. Bacteria can infect fish eyes damaged by injury. Treatment with a good antibiotic should cure these infections. Dietary deficiencies, such as lack of vitamin A, may contribute to poor fish eye health.
The most common cause of cloudy eyes in aquarium fish seems to be poor water quality, especially when the pH drops too low. In my years as an aquarium dealer, I ran many water tests for customers. When they complained of aquarium fish with cloudy eyes, almost without exception I found the pH in their aquariums to be extremely low. Often, the pH was so low it tested off the chart.
Large fish produce a lot of waste. One of the by-products of biofiltration in a tank is the production of acids. In a tank with a high bioload, biofiltration can produce a lot of acid. Over time, these acids cause the pH to drop. How fast this happens depends on the water chemistry of your local tap water, but with big fish, it tends to happen quickly.
Anyway, the solution is simple. Check the pH of your aquarium. If it’s below 6.8, and especially if it’s below 6.4, change more water more often. If it’s as I suspect, that’s all you need to do. The aquarium fish will heal right up without medication. If that doesn’t do it, choose one of the treatments above.