I have 6 discus that i've had for 3-4 weeks now in a 90g tank they have been doing great. One of them in the past 3 days has been getting very dark, since yesterday his eyes have gone cloudy. He is not eating anything and just staying in the corner at the surface. I have done a 80% water change yesterday and increased temp from 85F to 88F eyes are even more cloudy. All water parameters are perfect and none of the others are sick. What do i do?