I recently accuried a giant 10" pleco. My question is he keeps sticking his head out of the water why? Hes in a 40 gallon octagon with a giant peacful angle fish.

Generally when fish come to the surface it is for air. He may be having trouble breathing. Either he needs time to adapt to the new water or it is possible he has fill flukes , or has had some ammonia burn to his gills making it difficult to breath. Always address any issue with your aquarium by first testing the water. Check the ph , the nitrate , the nitrite and ammonia . Ofneverthing looks fine. It would probably benefit you if you used aquarium coops recomended quarantine meds. These will help.ensure he doesn't bring in any issues and also they can help cure him or her of parasites and infections. That's is where I would start . Hope this was help full . Also aquarium coop has a lot of really good videos on YouTube about these meds . Links to the videos can be found on their website.

I would call the co op directly and ask. They are very clear when explaining things. Have you recently checked your various levels? It could be thast something is a bit off and it didn't bother your angel fish. I've had that happen before.