I'm no expert but it looks like you might have some sort of insect infestation. I could be wrong. If you are watering it with plain tap water you might want to try using distilled water instead as tap water contains harmful chemicals like chlorine and flouride which are toxic to palms. Also, Assuming you haven't yet done so, you might want to repot it in the spring. It looks like you've got several individual plants in there and you can separate them if you want. I've had some areca palms for about a year now too. Here is a pic of one of mine. It's not quite as big as yours. I am very satisfied with how it has been growing. It's fun to watch the new fronds inch out a little further every day. Feel free to ask questions! - Jason

Yes i've using tap water, that i sometime mix with nutrition.
Might this be the problem, or simply the roots are too big for such a small vase and i really have to repot.

Anyway i think it's too late now to do anything. The situation got much worse than on the pictures two months ago. I'll be more careful next time.

ps: nice healthy palm you got there :)

It looks like spider mites. With is an easy fix. Use soapy water to kill them. love the 12 gauge shells too btw haha. I have about 30 areca palms in my back yard they make an excellent wall palm for fence cover. Also in the cooler months avoid too much water bud rot and root rot will destroy the palm.