HELP sick fish, new to this

[katejp]

HELP!

We recently changed the water for our black moor and added a pleco. Three days later, he is increasingly lying on the bottom of the tank and lethargic. He appears to potentially have ich? Which we are not familiar with treating. We have been lucky enough to have had a healthy fish for a long time and this would be our first time treating anything. Any help is much appreciated.
There are quite a few factors that are making us nervous
-Recently changed most of the water
-Added a very small bristlenose pleco
-Last week he had a pebble stuck in his mouth that required tweezers to remove... i worry i may have damaged his slime coat?
-The tank was previously washed with dish soap by accident. It has been rinsed incredibly well.

It's a real multifactor SOS.. Please help!
Pictures attached.

 

[katejp]

He had some movement and it looks like his back fins are a little ragged and have some red circles - I think we may have an issue with this new pleco.

 

[tlindsey]

How often do you do water changes? Did you add dechlorinator? Also was temperature of water added close to temperature of the in the aquarium? Yes possible Pleco may suck the slime coat of the Black Moor and stressing the fish.