I have an Oscar, I've had him for about 5 months and he's awesome, unfortunatly his buddy died about a month after I bought them both. However, the remaining Oscar's eye the past couple days seems to be a little bigger than usual. Just one of the eyes. Could this be the fish maturing or getting larger, or could this be some type of fishy cold? I try and do water/gravel cleaning/changing atleast once a week, the water temp may be 5-10 degrees a little cooler at times during the week than it should be, and the nitrite/ammonia levels are pretty low right around perfect. Help what's wrong with my Oscar?!