More improtant than the pH is the KH (carbonate hardness). The KH will
prevent pH swings, or at least severely restrict them. The carbonate
hardness is the ability of the water to absorb acids without changing pH.
For the pH Down to work, it first must consume all the KH before the pH
starts to change. Once the KH is gone, a pH crash is imminent. For a good
stable pond the pH should be above 80, with values of 100 being better and
200 or 300 not being unreasonable. Filters generate acids that consume KH,
and require resonable values of pH to function. So KH must be replaced
periodically. If your tap water has good KH values, this replacement of KH
can be accomplished by water changes which at 10% per week is needed anyway.
If the KH of the tap water is not high, then the addition of baking soda is
advisable.
--
RichToyBox
http://www.geocities.com/richtoybox/pondintro.html

wrote in message
news:1125493848.e09eb0ad4d5b35678ddb98cbd347caa0@t eranews...
Hi,

My pond is about 6 weeks old. I've been testing the water almost daily
and cannot bring down the pH to a safe level. It has been running
consistently at 9.0. Over time I have poured about 5 bottles of PH
Down and other pH lowering brands but with no luck. I test the water
around 6:00 am and some evenings.

The pond is about 2600 gallons with liner, 4' deep in middle, rock
bottom, 6' stream with 2 waterfalls, 4000GPH Nursery Pro pump, lava
rocks and plants in the waterfall box. My tests have been running 0
ammonia, 0 nitrite, 0 Salt, 9 wide range ph. I have 15 fish from 2" -
4" which seem active and healthy. I also have many marginal plants.
I've been adding a dry bacteria about every 2 weeks.

My water is very clear but with a greenish tint. I am worried this
high pH will harm my fish. I am a beginner and still don't know much
about ponds.

Thanks,
Lois