Hi: This is my first pond. 500 gallons with waterfall, EPDM liner,
planted (bogs, oxygenators, one small water lily), 2 shubunkins, 2
sarasa comets, 3 kois all about 4 inches. The fish and plants are doing
fine, growing great. The water is clear down to the three foot end but
slightly brown. Filtration is upflow through the waterfall (two bags of
biomedia and filter pads) and a TetraPond trickle filter with two pads
and bioball-type media with a UV sterilizer. The pond is about six
weeks old now and I've noticed the pH had begun creeping up to about ph
9.0 this past week (checked with both a pH color test kit and a portable
pH meter). During the day it fluctuates between about 8.5 in the AM and
about 9.1 in the late afternoon. Ammonia and nitrite are not detectable.

Do I have anything to be worried about? Should I be doing a water
change(s) or should I leave well enough alone since the fish seem to be
doing just fine.

Thanks in advance for your advice.
Joe