Raising pH

> I've setup a planted, 48 gallon tank two months ago and have
> let it cycle.  When I set up the tank I put in 8 black neon
> tetras who seem to have done very well through the cycling.
> I also  put in about 12 potted plants from 6 species
> (names unknown).
> When I first got the tank I tested the local water (I'm in
> Vancouver, BC) and found the following:
> pH = 6.0
> Hardness (ca, mg) = 0-10ppm (very soft)
> After discussing this with the aquarium store they said that
> I should raise my pH.  They gave me a 2 (1 lb.?) bags of
> dolomite (sp.?) and told me to add this to the gravel when I
> set up the  tank  They said nothing about the hardness.
> After setting up the tank and adding the fish and plants, I
> tested the water to be 7.4 pH.  This is way higher than my
> target pH (6.6-6.8).  Furthermore, when I do a partial water
> change  with 6.0 pH tap water, the tank shoots back up the
> 7.4 in a few hours.  When I talked to another guy at the 
> store about it, he said I put in too much dolomite in the
> tank and  recommended that I replace the gravel in the tank
> (!) and put 1/4 bag of dolomite per week until the pH levels
> off at the pH I want.  He recommended a pH of 6.6 for the
> fish I was  planning to get and to keep the plants healthy
> (CO2, etc.).
> After reading the Aquaria FAQ and the discussions on this
> list I have the following questions/concerns.
> 1) Is the dolomite solution recommended to me going to work?


> With such a low hardness, isn't my pH going to be too
> susceptible to fluctuations?


>  With the dolomite in the
> gravel I won't  have any way of regulating it's affect.

That's right.

> What are my other options for achieving a stable pH of
> 6.6-6.8?
>> other questions removed in the interest of brevity <<

I'm afraid the fish store gave you some very bad advice.  I mean, really,
really, don't ever ask them anything again advice.  The only time you want
to add dolomite to your substrate is when you want permanently high
hardness, high pH conditions in the tank. Someone else may want to
champion different numbers, but I wouldn't be surprised to see a pH of 
8.0 and a hardness of 150ppm in this tank after 6 months.  This is
appropriate for marine
tanks or for African lake cichlids, for example.  This is not appropriate
for a planted tank with soft-water fish like tetras.

For many South American cichlids and cyprinids (sp?) (e.g. tetras) a pH of
5.5 - 7.5 is tolerable to the fish.  6.0 may be just a little bit low, but
will probably be ok if the other tank conditions are ok (hardness, temp,
dissolved, O2, ammonia, nitrites, nitrates).  Personally, I wouldn't worry
about it at all, unless the fish show some distress.

If you want to raise the pH and increase the alkilinity (buffering), for
example, to stabilize th pH for supplemental CO2 injection, use sodium
bicarbonate (baking soda).  This will increase both pH and alkilinity, 
without increasing hardness.  It's possible to figure out how much to add
for a particular pH, but it's probably more reliable to add small amounts
until your pH is where you want it.  Check your pH when you do water
changes and repeat this procedure.  After a few water changes, you should
get it figured out.

You need to remove the dolomite, I'm afraid.  And don't ask those yutzes
at the fish store anything other than the cost of something.