With the beginning of summer it's important to remember that koi can get sunburn from the hot and longer summer days. Make sure your koi have some shade where they can escape the Sun's harmful rays. In years past I haven't had much of a problem as my pond is six feet deep. But this year my white platinum ogon is showing a lot of redness on it's side and a few of my lighter sankes are also showing red spots to a lesser degree. And it's only June. I had to put a 9x12 tarp over 1/3 of the pond to give them protection from the sun. Hopefully that will take care of it. Koi with a lot of white coloring seem most vulnerable. My darker koi aren't showing any effects.