For clarification the filtration is a Fluval FX4. I do weekly water changes 20-25% with gravel cleaning. Last changed this past Saturday. I've had the angel 8-9 months. They are not aggressive or started pairing yet that I can see. I feed them New life spectrum optimum flakes and pellets, with Fluval bug bites and frozen brine shrimp. Occasionally some freshwater mysis. Water parameter checked yesterday. Ammonia 0, nitrites 0, nitrates 20, temp 80 and PH around 8. Nothing added too recent, one fish added about a month ago. The angel is breathing rapid for last week. Almost like there is not enough oxygen in the tank, but I know that is not the case. No injuries that I can see. No spots, fungus, bloating, red marks on rest of body. Fins look fine. I noticed the red areas around the mouth a couple days ago. It's possible it's been there longer and I just noticed it in the smaller QT. It looks internal. The rest of the fish are unaffected. Thank you!