The hard and ugly part is over. We have scrubbed the algae off the walls to the best of our ability with wire brushes and we have power washed it too. I was thinking about refilling and acid washing it to kill off any remaining algae that may be lurking, then draining 1/4-1/2 of the water and re filling, then adding plants and fish. My concern is that some plants are grown into and under waterfall that cannot be removed, so how will acid wash effect these plants? They are Iris and cat tails. I don't know what level the Ph will be, as I would follow swimming pool procedures to do the wash and they don't have a clue what the Ph would be. Any suggestions?