Question
Help cloudy water pretty sure allege is ok. Water not green but on cascading waterfall my big rocks have a black coating over them.  Ive used water clear, murk for cloudy water, alegicide, allergy crystals. First of spring water was crystal clear but made mistake changed water to fix liner and wash sides and haven't been able to get it clear since. Have some plants water lily,  grass of some kind, little lettuce. Please help if you know what I need to do. And how often if and do I add salt.  Thank you Joanne

Answer
Only option I think of is of using clear chlorine on the rock and brush it(do not allow chlorine to go in pond since vegetation is present as you have written).
Can I suggest to you to installed a UV since the plants are growing as permanent solution.