Can anyone help? Three level pond. Fish only in lower pond. Having issues with string algae in top and middle pond. Middle pond is more like a stream and the whole bottom is covered in rocks…not fun. We’ve lived here for 5 years and this is the worse I’ve seen it. It sits in the sun all day. Not a lot of shade except for the lower pond. I’ve used sodium percarbonate before and that seemed to do the trick but I didn’t have this much. For 4000 gallons would I just throw in 4 lbs? Also, do I need more plants in the top pond? The middle pond is a stream, what would I put in there?