beta fish infection

Question
I have a beta fish and in about the past week i have noticed her left eye is twice the size of her right one... she can still move it and i think she can still see out of it but i'm wondering what is causing it and how i can fix it...
Thanks for your help
Tiffany

Answer
Hi Tiffany;

This is called "Pop-Eye". There are several causes for it. Injury to the eye can cause swelling. Internal infection  and a dirty aquarium are also possible causes.

Keeping the aquarium clean is the first step in prevention and treatment of pop-eye and related conditions. Make sure water changes of 25% are made every week to two weeks in aquariums with filters. Tanks with no filters need all of the water changed or at least 50% of it every week. Proper maintenance keeps fishes' immune systems working properly and lowers the chance of illness by diluting or eliminating harmful toxins in the water.

For possible infection and/or injury that led to infection, try a product called "Maracyn 2" by Mardel. You can get it at most fish stores. It gets inside the fish where the infection would be. (Most other medicines only treat the outside of the fish). Use it according to the package instructions. Often, the fish will lose sight in the affected eye. As long as the infection is treated the fish should live a normal life with only one useful eye.

Followups welcome.

At Your Service;
Chris Robbins