Re: NANFA-- pH

Bruce Stallsmith (
Tue, 13 Mar 2001 22:18:05 -0500

My doctoral dissertation was monitoring pond pH of two ponds in southeastern
Massachusetts, in part. Both of these ponds had low buffering capabiliy, one
in particular. We used a computer-guided data collector that read and
recorded pH every 10 minutes, running from March til November. Pond pH shows
very regular, sharp cyclicity during the peak of summer when photosynthesis
runs strong. Both of our ponds had daily variation of 3 pH units--5 to 8,
and 6 to 9 (sometimes 10). The high peak would come about 1-2 in the
afternoon in direct sunlight. Photosynthetic processes absorbed _all_
available CO2, and most of the bicarbonate HCO3- which has the effect of
changing the buffer equilibrium in a strongly basic direction.

Many lakes, in particular, show this pattern in shallow areas if one looks
closely enough. It probably doesn't affect most fishes for several reasons.
For one thing, it doesn't involve the stronger mineral acids. And for
another, a more important measurement of water quality is often total
dissolved solids (TDS) (hardness too, a separate but related measure) which
tells you a lot about the osmotic stresses on the fish's gills. More
immediate to a fish would be suddenly finding itself in much softer/dilute
waters, stressing the fish by causing it to lose ions through its gills.

If you have a heavily planted aquarium you can probably observe this
phenomenon yourself. Check your tank pH at 5 a.m.(!), and then check it
again at 2 p.m. You'll probably be surprised at the magnitude of the pH
difference (remember, it's a logarithmic scale!).

--Bruce Stallsmith
Huntsville, AL "have pH pen, will travel"

>I remember that when I tested the water your Elassoma zonatum came in.
>Those conditions are typical of my rain barrel with a thick coat of hair
>algae on the inside. This is probably because it's rain water which is
>soft but poorly buffered. Yet the single bluespotted sunfish I stick in
>there every year seems to thrive in this caustic environment.
>Soft but alkaline- sounds like a paradox but possible when you have
>poorly buffered water and lots of plant life. Plants and algae drive the
>pH up when they crank out oxygen. This used to happen with my pond
>before I started using pine and then barley straw. In the AM pH readings
>would start out in the low 6s and rise as high as 7.4 on a bright sunny
>It has been said this is not good for the fish - but surprisingly mine-
>including blackbanded sunfishes have survived and even reproduced
>despite these radical swings.
>If you want to raise fishes that require or benefit from alkaline water
>the best way to stablize the pH is to use gravel derived from limestone
>in the pond and maybe crushed oyster shell. Or the same in your
>biofilter. For acid loving fish use peat or pine needles or barley
>straw. Both minerals or tannic acids ironically serve the same function
>of stablizing pH. When using organic substances like barley straw -
>which is also used for algae control - it is a good idea to remove it
>from the system before it decays or else it will contribute nitrogen and
>phosphates that fuel algae growth.
>Jeff fro PA

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