Bottom feeding fish dying

[MikeS]

Is it possible for poor water circulation to contribute to the death of plecostomus and cories? All the other fish (african cichlids) are fine. If the water isn't circulating well enough, can accumulated waste at the bottom of the tank cause there to be toxicity near the bottom that kills off fish like cories and plecos?

 

[Feline]

Or they can't get enough food? What kind of food are you feeding them? Plecs need algae wafers and cories need sinking food.