Cement Pond Plants ID

Ah, OK. That makes sense then. Silt, decomposed vegetation, and fish waste would all be components of a soil, which could be a very nice soil indeed. When you said "stones", I was thinking more like cobbles. I guess what you are describing is more like an undergravel filter, no? Sounds pretty cool to me. Maybe the cypress is just having a hard time due to the pH then - you mentioned that it is alkaline? If the yellowing is due to actual chlorosis, then the fertilizer bucket may or may not work - the tree would need more iron, which would become more available if the pH were lower. But maybe if enough iron were added, it could overcome it.

I love your pond. I am always jealous when you post photos!