discus - possible HITH

Hi,
I bought 7 discus 2 weeks ago. One of them did not make it. The reset
are fine.

I noticed one of the remaining discus now have tiny holes in the head
area, not really big and they looked more like air bubbbles. I'm worry
this one may have the HITH and will get all other discus in trouble.
The fish is fine otherwise, eating like crazy. They are all about 2.5
in big.

I change 45% of water every 3 days or so. My tank is 125G and has some
plants in it. Other tank mates: 1 cat, 2 plecos. PH is about 6.9 to
7.0, no ammo, temp 85-86 F

What should I do? Any tips?

Thanks in advance!