Many water systems add some sort of hydroxide (alkaline) to reduce
corrosion. Mine adds sodium hydroxide. The tap is 8.9+ but drops rapidly
once out of the tap. Aging the water generally will help.

yeah. straight out it is like 8.2.. after two days aging, it's like 7.8...

As for adjusting kH without affecting pH, the answer is no. Up the kH the
pH goes up, unless you add CO2 to balance the pH. You can also use an
acid buffer to drop the pH while raising the kH.

so.. add kH increase chemical, and also put in pH down or something?

does this mean people stop CO2 during the night? wouldn't it
over-compensate by producing too much CO2? I guess one way to fix this is
get a peumatically actuated air intake valve that is timed so that when the
lights go off, it will turn on venturi in the tank, to bubble out CO2?

sigh. I guess I have too much plant for my tank and water condition, I
guess :-(

Out of curiosity, does your pH tend to drop consistently between water
changes? In my Pre-CO2 tanks the kH and pH would slowly drift down over
time, actually it still does.

well, this is a hard question to answer... mainly because my tank seems to
experience quite a bit of pH fluctuation over the course of the day.

1. when the tank was much newer (yes.. my tank is about 4-5mo, so..it's
still pretty new), the pH seemed to stay pretty stable around 7.6-7.8. very
alkaline, and the water was more yellow due to all the tannin leeched by the
bogwood. also the water was always slightly cloudy (this was true even
without the plants). stale water out of the tap is about 7.8, so I guess
this made sense.

2. now the pH drifts between 7.0 and 7.5 (7.5 at night, 7.0 in the morning)
probably due to plants eating up CO2. water is almost clear (no yellow),
and very very little haze.. (you can only see the haze at night with no
ambient light).

3. ever since I noticed this inter-day pH drift/cycle, I have not seen my
water go above 7.6... yet... and I just did a 50% water change.. and within
two days, it's back to 7.0-7.5 daily pH drift... (yes.. poor fish)..

I don't use any activated carbon, so I guess the tannin was just
water-changed-out over time... my water change is on the order of once in
1.5 weeks, about 25% (NetMax warned me that since the tap pH is high, and
KH/GH is low, if I lapse on my water change the pH differential may become
so large it may be bad for fish.. not to mention potential pH crash due to
limited buffering capability). at any rate, right before my 50% water
change, the water pH cycle was 7.0-7.4 or so.. now it's like 7.0-7.5.. so I
guess you can say it is slightly higher.. but not noticably higher for the
amount of water that got changed out. (value between 7.2 and 7.6 is like a
guessing game anyway)

the overall drop in the pH may be because I've started to add some plant
nutrients (Flourish, flourish excel, flourish iron. my swords started to
look downright pale, and new anubias leaf was almost white! now its all
nice and green..)... so it's possible the plants are all of a sudden doing
so well that it's depeleting CO2 to quickly compensate the pH differential..
or whatever.. (I'm brainstorming here).

linda