On 31 Mar 2004 14:14:16 -0800, (NewbieBill) wrote:

It appears to be bass ackwards. As far as I can tell from my narrow
range on the scale it was once again 8.8+ at 10 am and 7.8/8 at 3 pm.
Would water hardness (which I can't currently measure) make any sense
of this. I would guess our water is a little hard, but not sure.

There are two hardness measurements GH or general hardness is usually
a reading of calcium and magnesium. KH or carbonate hardness
measures the buffering agent in the water that keeps the pH from wild
swings.

Plants use sunlight and carbon dioxide to make food and release oxygen
during the day, but oxygen is used at night when the sun isn't shining
and carbon dioxide is released into the pond making carbonic acid,
which lowers the pH reading at night or early in the morning.

Before you use a pH down agent check the KH, or try baking soda first
if the pH is too high. Baking soda, sodium bicarbonate, is a great
pH buffer.

http://srac.tamu.edu/464fs.pdf
http://www.drhelm.com/aquarium/chemistry.html

Regards,

Hal