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re: driftwood & pH

>From: "Jennifer Orme Van Buskirk" <J.VanBuskirk at m_cc.utah.edu>
>
>Could a piece of driftwood in my 135 gallon tank be buffer my pH at 
>7.6?  

I suppose the driftwood could have soaked up enough carbonates to buffer the
water upwards.  I'm not sure about this, but isn't limewood an alkaline wood?

Check the carbonate hardness of your tank water.  If it's still at < 10 ppm,
then you probably aren't getting much of any buffering from anywhere.  If it's
more like 90 or more ppm (normal for Dallas), and you're changing your water
with 7 ppm water, you've got something buffering your water.  (BTW, 90 ppm
isn't too high for most plants, but I don't know about discus).

>1-  not nearly enough co2 is being dissovled in the tank, so increase 
>the amount bubbled in the return line  (an idea I don't like because my tank
>houses 4 
>almost full grown discus who at last if I remember breath oxygen and 
>not carbon dioxide), or hook up in my tank the ugly co2 diffuser 
>that came with my sandpoint co2 tank to try and diffuse more of the 
>gas that is being let out. (those of you who have one know 
>what a big green ugly monster it is, not to mention you have to hook 
>up a powerhead to it)

The big ugly monster is probably a sandpoint CO2 reactor that completely
dissolves the CO2 in the water.  If you find that your carbonate hardness is
still relatively low (less than 2 dH (18 ppm per dH)), then you simply aren't
dissolving enough CO2 to keep up with either loss or your plants.  If you
aren't dissolving enough to keep up with loss, you shouldn't see much in the
way of diurnal pH swings.  If you aren't keeping up with your plants, at that
low of a carbonate hardness level, you'll probably see some pH swings.

If you decide that you aren't keeping up with loss, you can try to:

1.  Increase the efficiency of the dissolution by installing the reactor or by
increasing the surface area/time interaction between the CO2 bubbles and the
water.  

2.  Decrease the CO2 loss by decreasing air/water interaction (surface
agitation, airstones, biowheels, etc.)

It's true that your discus breathe O2 and not CO2, but the CO2 content in the
water doesn't affect the O2 content in the water, and the only ways that your
discus can be harmed by the CO2 content are:

* pH problems: Either swings or extremes (I'd pay close attention to this with
  such expensive fish in a tank with low alkalinity).  I'm of the opinion that
  non-phosphate, weak acid buffers might be useful in a soft water tank to help
  control the pH.  This opinion is based entirely on lack of experience, so 
  you'd do well to research this matter further before taking this as advice.

* suffocation: If the CO2 content of the water exceeds the maximum CO2 levels
  of fish blood, your fish will not be able to "exhale" enough CO2 to control 
  their blood pH.  (That's the way I understand it.)  Dangerous CO2 levels in
  an aquarium are in the 30 ppm range from what I've read, and if your water
  has < 10 ppm alkalinity (carbonate hardness), its pH would be less than 4.5
  at 30 ppm CO2.  CO2 levels up to around 15 ppm are nice to have if you can 
  control pH swings.

David W. Webb
Enterprise Computing Provisioning
Texas Instruments Inc. Dallas, TX USA
(214) 575-3443 (voice)  MSGID:       DAWB
(214) 575-4853 (fax)    Internet:    dwebb at ti_com
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