Chinese Algae Eater- Sick

Question

"Monster"   I have a Chinese Algae Eater that is about 2.5 years old and just over 6" long. "He" has always been an extremely healthy fish and has survived quite a few tank catastrophes in the past (one time he was the only survivor, so I know he's tough!) He's been dubbed "The Monster" due to how big he was compared to all of my other fish at one point and his knack at surviving. He likes to spend most of his time behind the filter of my tank, but usually comes out later at night or when things are quiet to eat and really enjoys algae wafers. Since he spends a lot of time mostly hidden and is fairly shy, I have not noticed him declining into the fish I just saw. He's skin & bones. He's so skinny and I've never seen him like that. I have not changed his diet- my 30 gal tank mix of a few loaches & barbs eats a rotation of frozen brine shrimp, bloodworms, flakes, pellets, & wafers- but I did add some larger rocks to the bottom of my tank a few weeks ago. I was wondering if possibly his wafer/pellet foot has been sinking into the rocks after dissolving and he can't reach it? He seems very quiet, and his topline is completely sunken under his spine from head to tail. He's also staying on the floor of the tank & no longer behind the filter, I don't think he has the energy. This fish used to look like a sausage and I don't know how to help him. I JUST noticed this so first thing in the morning I am going to contact the local stores and see if they have any advice, but I'm just heart broken and want to help him as soon as possible. Other than being a bit, but not severely listless, and extremely skinny, he looks normal. His color is still bright, he has no fungus/flakes/swelling/spots/etc. My tank only has fake plants and he has been fine without real vegetation, but I was considering getting a plant to help? ANY advice, as soon as possible would be so greatly appreciated. Thank you!

Answer
Alex,
What concerns me is the rocks you added to the tank. The algae eater loves to go on rocks and other decorations in the tank. When you added the rocks, did you boil them for a few hours first and then let the cool before adding them? I am thinking its the rocks. I would remove the ones you just added and do a small 25% water change and see if he gets any better. When we have healthy fish that suddenly start going downhill, we have to think of things that have changes. Let me know how he does once the rocks have been removed.