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Fish Cloudy Eyes

Do you know what causes cloudy eyes in aquarium fish, and is there any way I can treat it?

By Mike Wickham |

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fish cloudy eyes
Several things can cause cloudy eyes in aquarium fish.
Q. 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?

A. 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. For example, did you know that a 10-inch oscar is the equivalent of 1,000 1-inch oscars? (It's 10 times as long, 10 times as wide and 10 times as high.) 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.

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Reader Comments

cheryl    livermore, CA

6/30/2014 5:44:29 PM

If my sucker fish has cloudy eyes does it mean its dying?

Chuck    Athens, AL

6/16/2014 11:55:18 AM

This is helpful for people that know their ph has dropped due to things like say, driftwood which if added unprepared like mine was will drop the ph, and cause eye cloud. This happened to my blue gourami.

Albert    Norfolk, VA

4/25/2014 2:40:45 PM

I have to agree with Taylor from Atlanta, I don't think the comparison with the Oscar dimensions is accurate. My tank became overloaded with algae and when I did a complete water change that's when I discovered my fish had cloudy eyes. I hope with the water change and the slime coat medication it clears up.

taylor    Atlanta, GA

4/23/2014 5:57:49 PM

I have to disagree with the comparison between the 10 inch oscar and the 1,000 1-inch oscars.

If you had one 10 inch oscar you would feed it a few large pellets a couple times a day. If you had a pond with 1000 oscars you would have to throw handfulls of food a couple of times a day. The bioload cannot exceed the amount of food you add!

Mathematically, fish are not cubes, which is how you're treating them in your evaluation. a ten inch oscar isn't 10 inches wider than a one inch oscar. for simplicity, let's pretend the one inch long oscar were also an inch wide, you're saying that your 10" oscar in the example is 10x as wide. Have you ever seen an oscar 10" across? No. They don't grow the same rate in every direction.

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