High Ph

I will probably be posting regularly for a while untill not only my
pond is in balance but my understanding of it all I have been
bringing this pond back to life for the first time, for me. I am in
sunny Austin, Texas. I felt like I was making excellent progress with
the 'health' of my pond till the last 3 or 4 days. Since then I have
noticed String Algae developing (water is clear) and my ph rising
steadily. Ammonia, Nitrates are at 0, Nitrates minimal if any. Don't
have a hardness test. While I haven't been testing it very long I
felt like my ph WAS normally around 8/8.2, apparently about the norm
around here. Now I am getting readings at bottom of my chart which
only goes to 8.8 and I suspect my color is higher than that. I may
have done (at least) 2 things wrong. Most of my numerous plants and
lillies have only been there a few weeks. When I potted them I did
use a topsoil mix which had no vermiculite, fertilizer etc. but was
somewhat loamy, sandwiched top and bottom by pea gravel. Perhaps no
coincidence 2 days after building a little in-pond stack of river
rocks and Moss Boulder to create a simulated waterfall splash (from my
outflow pipe) I noticed my ph rising (also so did the temperatures and
sunlight). I have been using the same material to raise my pots. So
I guess this post I am soliciting advice as to a direction to attack
first. Most likely the rocks, soil or other things. My first 'bloom'
I really panicked and I don't want to repot all my plants, put them on
what and take away my waterfall, if this is just a balancing thing
that requires smaller adjustments. Thanxx - Bill