The pH has been fairly stable from day to day and is ranging from 7.5
in the AM to 8.5 at the end of the day.

Unfortunately that isn't stable. Your change should only be about 7.5 in
the AM to a max of 7.9 in the PM. The problem is your low KH/buffering, as
you mentioned, not the plants.

The KH has been ranging from 89.5 to 107.4. What I mean by stable is
that is always about the same when I measure it at the same time each
day. Our water is completely soft, so I have been trying for a long
time to get both the GH and the KH up and have been using sodium
bicarbonate as a temporary booster till I can get enough GH in there
to hold the buffering capacity up long-term. I've been seeing the
wide diurnal pH swings even when my KH was 100, so I am thinking
that the effect of photosynthesis (CO2 consumption) during the day
accounts for the high pH at the end of the day.

The whole dolomite/mud thing happened because I was trying to get the
KH up. :-( I figured I can't keep dumping NaHCO3 in there
indefinitely, because eventually the HC03 will get consumed and I'll
end up with too much Na in there. I've been adding an awful lot of
baking soda in there since the pond was built 2 years ago.

Joan

This is also why the algae is blooming and
why the mud is not settling. Get the KH/buffering up and things will settle
down/out.

What is the KH of your tap water? If that is good, do a slow flow thru if
you can, otherwise 10% water change every other day will not hurt the
balance.

A flow thru system, with carbon filters on the new water, is being highly
recommended in the koi community right now. Where about 10% exchanges over
a 24 hour period. This isn't for everyone, especially if your tap water
isn't great, or water prices are high. It's more a high-end koi keeper's
ideal. I personally have an accidental flow thru, some small leak that
drops the level about an inch/day, so I add water when I get home.... I'm
still doing a 20% on the weekends.

IMO, I'd be using baking soda to get my KH up. About 1 cup/1000 gallons and
retest. That pH swing is harder on your fish and filter than adding baking
soda. ~ jan
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2Zone 7a, SE Washington State
Ponds: www.jjspond.us