Humu Humu Trigger acting weird?

[Ksm675]

Hi all! My girlfriend bought me a Humu Humu Trigger from a LFS, a reputable and well known one, Sunday morning. I properly acclimated him to the tank and he seemed fine swimming around all day Sunday. Monday morning I wake up and check the tank before work as I usually do and he was sitting on the sand bed under a the live rock and hasn't moved since. He ate a little brine shrimp Monday night only because I target fed him. It is a 75 gallon tank with a wet/dry filter. All other fish are doing fine and have not had any issues in my tank ( tomato clown, Singapore angel, some kind of tang, and 2 pajama cardinal) any help would be appreciated. I checked this morning again and he was laying on his side near a rock.
pH 8-8.2
Ammonia - 0
Nitrite -0
Nitrate - roughly 5

Ive attached a picture.
(https://i.imgur.com/8gFS3e2.jpg)

 

[Deinonych]

It could be a number of things - stress from a new environment, bullying from another fish or possibly disease. You may want to consider a quarantine protocol for new additions. Quarantine allows the fish to acclimate to captive life and enables you to identify and treat possible diseases before the fish is introduced to the DT.

 

[Ksm675]

I've been debating on it but haven't gone through with it because I've never had an issue in years of freshwater and about a year of saltwater. He hasn't been bullied by anyone in there I'm assuming he's stressed.

 

[Justfebreezeit]

Is he twitching his head or any other symptoms? Breathing heavy?

 

[Ksm675]

Is he twitching his head or any other symptoms? Breathing heavy?

No, he doesn't seem to be breathing heavy or twitching he just isn't active and sitting/laying on the sand and rock.