My Oscar eyes are blurry

Question
I have two Oscar that been with me since they were around one inch. I been up grading my tank and now I have a one around ten inches in a 75 galon tank and the other one I just separated because he develop hole in the head, this one is a 50 galon water tank he is a little smaller. The ammonia nitrite and ph are fine. I change like 50% of water once a weak and I have bio filter in the tanks..Please help me I don't want to loose them and the one that is in 75 gallon develop something in his eyes they are blurry the other on has hole in the head. I feed them raw shrimp, dried shrimp and pellets. I feed them different things, I also add salt to the water...what caused the hole in head?

Answer
Hi Noemi;

Test the tank water for the levels of nitrate. It's the end result of biological filtration and thought to be a major contributor of HITH (hole-in-the-head) as well as causing or contributing to other chronic health problems. Knowing the ammonia, pH and nitrite is good but nitrate can't be left out of the mix. Diet is a major consideration too. Even when we think our fish get a well-rounded diet there may be important nutrients missing. Supplements can help correct vitamin deficiencies and at the same time switching to a higher quality pellet can start getting them back on the road to recovery. Here is a good web page about HITH and it's possible causes and treatments;

http://www.flippersandfins.net/HITHarticle2.htm

At Your Service;
Chris Robbins