Help me.

My fish are dying at a rate of 2 - 3 per day. I don't know exactly why.
But I suspect it is a combination of temperature and pH. (pH around 8.0)
How I don't know...

My pond is in full sun and can get quite warm above 80F easy. But now the
pond is cooler sense the outdoor temps have become more tolerable. Anyway,
I noticed I was loosing some fish. I tested the water and everything came
back OK except the water hardness, and pH. Both were way high. like a pH
of 8.0. Ammonia and nitrate levels were great. Hell, I've even noticed the
string algae that started to grow dropped deader than a hammer as well!!!!
Something is in my pond water and its killing my fish.

Any ideas? Can temp cause a high pH level? Should I make my pond deeper
because its in full sun and can get quite warm? The current depth is 18-24
inches and approx 250gal. I had about 20 goldfish averaging 3-6 inches in
length. I'm down to about 8 and they're moaping around like the grim reaper
is on their shoulders.

Help!!

PondDiver