Sick (dying) bristlenose pleco? Please help!

Sorry to here your new fish isn't doing so well. I wonder if he may be getting picked on by some of the other fish and is getting stressed out? I have a Medusa, 8 years old. They like a nice safe hidey hole to protect themselves. Some 2" or 4" PVC. Naturally they hide under flat rocks. They are sort of nocturnal, so hiding during the day is kind of normal for them. They like a lot of water movement too. When a fish shows signs like that we tend to mess with them to check up on them, which only makes it worse. Since the rest of your fish are ok it may not be a water problem. They like soft water. Your pH is good so the softness should be fine. The one thing all Plecos love is romaine lettuce. Put a whole big good looking leaf in the tank. It will take a day or so for it to soften up a bit to become edible. They should go for it at night after dark when the other fish become dormant. They hang upside down under the leaf feeding on it. You will see little holes everywhere on the leaf. Pull it out before it breaks down and clogs your inlet. You can pretty much keep a leaf in there at all times. They like it a little warm. You may want to go up to 78-79 to see if that helps. They also love it right after a water change, you will see them come out and enjoy the fresh air. Hope this helps. Try not to bug him too much, and follow that advice and he should be fine. They live 7-10 years.

Definitely make sure your fish is getting good water movement. They require a lot of oxygen. Naturally they live in streams, so they don't do well in still water. Wanted to emphasize that. Sorry to ramble on. Hope he bounces back!

My Medusa Pleco: