Chadman, Aluminmum Sulphate (Alum) will clear and floc out most solids in your water includin planktonic algaes.

If your water is "dark" it may be stained from tannins released as leaves decay instead of clayy. Since you had your pond dredged, I presume there is a fairly heavy load of debris that enters your pond.

To see if Alum will indeed clear your water, go to any grocery store's spice section and purchase a small container of Alum (used in canning veggies to keep them crisp. Sprinkle a pinch or three into your test jars and shake well. Let the jars sit for a coouple days and if the "dark" is from solids, your water should become crystal clear. If the water clears, you can do more testing to see just how much Alum is needed to clear your pond.