"linda mar" wrote in message
...
very bright halogen light), and when in doubt, I always create the control
specimen, which is measuring the pH of my tap which is really high in pH.
there is a marked color darkness difference between very high pH (using
tap
water), which does reflect the 7.6 color on the chart. but what i get is

The most likely reason that your tap water has a high pH is that it's low in
CO2. The CO2 level of the water straight from your tap might be variable at
different times. That's why such a reference sample is unreliable. You
should let a cup of water sit for a while, or aerate it, before taking its
pH. At KH of 2 degrees, your pH at equilibrium should be about 7.2. That
applies to both tank water and tap water.

How wide can the plant-respiration-induced pH fluctuation be? can it
really
go from 7.0 to 7.6? (37G, moderately planted...)

It sounds like you have plenty of agitation. But if there wasn't enough, the
plants could easily bring the pH up to 7.6. That only equals a 2 ppm drop in
CO2 from equilibrium. Of course, the plants would consume more CO2 with
higher lighting. How much light do you have? Any sunlight entering the tank?

there is a tremendous amount of surface ripple caused by total of about
400
gph water being spurted towards the surface (enough to suck down some air
into the tank where the different current meet.. sort of like a mini
vortex
going on...), so... (lots of current in the tank...). may be I should
switch the HOT Magnum to trickle-type power filter? would that give more
gas exchange due to cascading water? (lower flow rate than the HOT Magnum,
though)

As I said, it seems like there is more than enough agitation from those 3
sources.

no. GH went *up* from 2 to 6... and no.. I have no rocks or any
mineral-creating stones in the tank (just some bogwood and the standard
inert aquarium gravel). There has been some explosion of snail population
which makes sense (higher GH supporting more snail shells..).. but I don't
think I have done anything purposefully to increase GH that I know of
(other
than potentially the tap water had a very high GH one weekend or
something),
unless those seachem flourish, flourish excel, flourish iron adds to GH (I
e-mailed them and they said it should not affect it)

Okay, I misread that part. It might be due to snails dying and their shells
melting, but I'm not as certain about that. Or it might be the way you're
reading the GH kit results. I have a hard time with my AP GH test kit. The
color change from greenish-yellow to green is too subtle. Sometimes I miss
it and keep adding drops of the test solution.

Anyway, I think a large water change would greatly help reset the water
parameters, and balance things out. Change perhaps 50% of the water, and see
if the GH, KH, or pH start to drift again. Make sure you take the pH
readings at the same time each day. Then test the water at different times
on a single day to see if there are any daily cycles.

wouldn't adding baking soda increase the pH of the water? if the water is
already at or close to 7.6, I don't think it's such a good idea to
increase
pH further (esp for the fish)... are there other means to increase KH
without increasing pH?

Yes, more KH will increase the pH, but if the water is at 7.6, it's for some
other odd reason. If the KH is 3, for example, the equilibrium pH at that
level should only be about 7.4. But find out exactly why it's 7.6 before
adding the baking soda. A way to increase the KH without affecting the pH is
of course to inject CO2. The addition of CO2 can offset the pH increase due
to higher KH.
__
Alex