Hi Jason, sorry for the delay in response...I've been working nights. Regarding the pH question: bodies of water, ponds, lakes even many aquariums experience pH swings every 24-hours. This is primarily due to photosynthesis. So it would be a good idea to take several readings (morning, afternoon and evening) for several days to get a real sense for the pH of your lake. You have an open system vs closed system. Ponds are closed systems in that they do not receive or empty water unless done so by mechanical means. But you have a scenic water feature and flow through natural water which is something many of us would die for! The land surrounding the water is beautiful too. You asked what I would do. Given that it is really a lake, I would do a little housekeeping around the shoreline and then study the physical characteristics of the lake. Specifically, the depth and determine if there is a channel running through it. Then, rather than trying to manipulate the pH or flora and fauna, enhance what naturally lives in your area. I would probably install an aerator system (pump and air diffuser) if there is sufficient depth. Either one of those air diffuser systems or a decorative fountain would do nicely. From experience, they work great. What you have is a gorgeous estate lake and that would help keep the water turned thus reducing algae blooms etc. I think you mentioned there might be excessive sediment on the lake's floor. The easiest way to deal with that is to have a company come in an pump out the sediment. Again, from experience, (School of hard knocks!) it is expensive but will give you a fresh start. Just make sure they carry away what is pumped out and don't let them discharge it in the surrounding area where it might make its way back into the lake. Your local aquatic center can really help you out with all of this and I think you are wise and should be commended for seeking their assistance. Anyway, just my two cents worth.
Stephen