Discus swimming on top of the tank

Hi,

I have 12 of 3 inch discus for the past 4 months. I brought them when they were less than a inch. They all seem to be doing fine except for a couple of runts.

Today morning, I noticed, one of them is swimming at the top of the tank. It looks healthy and all, but looks very weak and didn't eat the entire day as well.

My water parameters seem to be ok. Ammonia - 0, Nitrites - 0, Nitrates - 40 ppm, I am doing a large water change. Anything else I am do?

I am posting a picAttachment 112636. Please advise

Do you age your water? When they go to the surface, it is usually suffocation. Something in the water change? Dissolved gases in tap water? Is there plenty of surface movement?