pH adjustment

["Darren J. Hanson" <djhanson@calweb.com>]

> A recent thread considered the use of muriatic acid to drop pH. and
> hardness , isn't the by product of this.treatment sodium chloride? Does
> this go for the phosphoric acid too . Is it stable ie - bounce?

Well, Muriatic Acid (HCl) is going to neutralize some of the bases in your
solution and pull the pH down. Available alkalinity will then try to pull
the pH back up. By continually adding small amounts of acid, you will cause
the pH to drop and then bounce most, but not all, of the way back along with
an associated drop in total alaklinity. If done in a separate container, you
should be able to repeated dose a large container (50 gallon drum? 100
gallon fish tank?) with acid and eventually deplete the alkalinity to the
point that you can make "permanent" adjustments to the pH. (Permanent is in
quotes because as soon as the fish start excreting ammonia, you feed them,
you add plants to the system, top off a tank, etc, you'll be readjusting the
alkalinity and pH again.)

The reason I suggested Phosphoric Acid (H3PO4) instead is that after it
disassociates, you'll be adding phosphates to your water instead of
chlorides. I don't remember if you described your complete setup or not, but
I thought you had mentioned raising plants of some sort which I figured
would be pretty starved for Phosphorus due to it's tendancy to precipitate
out of soultion at high pH.

In response to your question about sodium chloride, what would be formed
depends primarily on what the predominent mineral is. You could as easily
form Calcium Chloride, Magnesium Chloride, Ferric Chloride, etc.

As far as stability goes, once you've adjusted the pH appropriately, it
should be fairly stable. Of course, it'll take some time to learn how much
acid you need to add to deplete the alkalinity enough to make the pH
adjustment in the first place.

What I was envisioning was having a storage tank at least large enough to do
your regular water change, top off, etc. It sounds like you have about 720
gallons so if you do a 10% water change on a weekly basis, you'd want at
least a 75 gallon storage container. Larger is definately better, however.
Then, you could connect a pH controller to a dosing pump similar to those
used by marine aquarists to add Kalkwaser to their tanks. I'd also
reccommend a powerhead or similar small pump to keep the water circulating.
When the pH is above the point you set, the dosing pump would slowly add the
acid. Eventually enough acid will be added to deplete the alkalinity and
allow the pH to stabalize at your new set point. At that point you can
siphon your tanks however you want and top them back off using a sump pump
submerged in your storage tank. When you're done, refill the storage tank
with tap water and add dechlorinator or any other additives you desire.

A similar technique would involve using clean (no pesticides or fertalizers)
peat in a canister filter on the storage tank. The peat will leach tannic
acid and have a similar net effect and possibly more closely simulate the
fish's natural environment. You will have to replace the peat on a regular
basis and it will have a tendancy to color the water unless you also filter
with activated carbon to absorb (and/or adsorb)  the disolved organics that
stain the water.

Whichever technique you use, I would caution you to NOT treat the water in
the individual tanks as that will cause a repeated bounce of the pH that
will stress the fish. By treating a separate storage tank, you can add fully
treated water and not have to worry about bounce.

- -- dj