Hello Lorraine101, welcome to the joys of having a pond, in order to help, I need some more information please.
What are the physical dimensions of your pond?
Length width and depth
What is the make and model of your pump?
What is the make and model of your U.V.
How Long do you leave the pump and U.V. running for?
What is the make and model of your bio filter?
What did you do to support the purple slate? (previous post)
Any chance of a picture of the pond, it would help immensely.
I presume you still have no fish?