How can I care for orchids? I want to use natural treatments...

Just use a horticultural soap.Make sure when you spray not to spray the flowers just the orchard medium.

Orchids need ample water but should be allowed to dry out some between waterings. One way to check for watering is by poking your finger about an inch into the growing media. If it’s dry, give it some water; otherwise, let it be.

Also- you should repot every other year.

Read more at Gardening Know How: Orchid Growing Tips: How To Take Care Of Orchid Plants Indoors https://www.gardeningknowhow.com/ornamental/flowers/orchids/indoor-orchid-care.htm

I always use soap and water and for especially tough critters (scale) I use Neem oil which you can buy at health food stores. :)