Midas with reddish/pink gills

[JRT83]

So I was stressing my fish out yesterday because I returned my umbee to the LFS so I had to take alot of the decorations out and chase the umbee around til I caught him. I woke up this morning and noticed my Midas' gill plates are a lightish red/pink color (1 side way more noticeable than the other) and he's had white stringy poop. Called a few LFS in the area and 1 guy said it could be from dashing around the tank and injured himself and someone else said an ammonia spike from disturbing the gravel and kicking up any excess food/debris. Any ideas as to what could be wrong and what would be the best treatment? He's about 3-3 1/2" long right now, everyone else looks and is acting normal. just did a 40 gal water change and dosed lightly with aquarium salt.

125 gallon tank w/ 2 biowheel 350's and 1 Aquaclear 110 (up/running for a little less than 2 yrs)
2 30 gal water changes a week
78-80 degrees
Feed new life spectrum pellets daily with a treat of shrimp or krill once a week

6" jaguar
4" salvini
3" midas
2" festae
4" featherfin catfish

Water always is in good shape
Ammonia: between 0-.25 ppm
Nitrite: 0
Nitrate: 10ppm
ph: 8.2

Sorry for bad picture quality