I have about 3 year old Koi that about a week ago developed white large whitish spots on their body. It does not appear as on top of the scales but rather inside. I first thought it was scraped. Koi is very active, eats and behalves as usual. Local pond shop recommended salt baths to treat for ulcer or parasites. They also recommend to introduce salt into pond itself.\nPond is about 1500gl, 4 years old with plants. Filtration and waterfall working 365, 24/7. Water tests show slightly elevated and high hardness. Total 8 kois I don't see anything unusual in all others. They slightly off colors but I attribute this to coming from winter.\nI have not done water change yet or any additions. Have UV running. A month ago vacuumed bottom and added water. Water is added through chlorine-removing filter. Added some anti algae treatment\nCan you please help me identify if this is a disease indeed and safest way to treat it. On the photo it is orange with black, black eyelashes koi. It is our favorite.