Date: 05 December 1998
From: Adrian Desbarats <adesbara@ns.sympatico.ca>
To: AQUA-L@killick.ifmt.nf.ca
QUESTION:
Does anyone have any experience with increasing the pH of seawater by metering in sodium bicarbonate or some other buffer? Are there any companies with experience in this that are also capable of setting up such a system?
Adrian Desbarats
Marine Biologist
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COMMENTS 1:
I think we need a little more information before proceeding. What type of system are you talking about (finfish, shellfish, size of system)? A small description of the system would be good. Why are you trying to raise the pH? If you have a finfish system that has a problem with the pH going down, then you may have a carbon dioxide problem. In this case, metering in a buffer is not the solution, aeration is. If on the other hand you're simply trying to get to some pH to trigger a spawning or something of the like, then you might try something like a Blue-White Industries metering tank. (http://www.thomasregister.com/olc/bluewhite/)
Trying to meter in sodium bicarbonate can be done, but it's a little tricky. Trying to keep enough quantity of sod. bic. in suspension in the metering tank is difficult. It's almost easier to do it manually.
Mike Christensen <mchris@unix1.sncc.lsu.edu>
Mike Christensen
Research Associate
Louisiana State University, USA
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COMMENTS 2:
You can increase pH in large volume saltwater systems (over 150,000 gallons) by dumping in 25 lb increments from 50 lb bags of sodium carbonate- not bicarbonate. Bicarbonate will buffer the system, but carbonate will actually do more to increase the pH, which is what you want. In large systems, you can dump more in, more casually, due to the shear size of the system.
I had a sump basin that allowed the NaCO3 to dissolve at its own rate as the water rushed by the salt mass on the bottom of the basin. It did not create a high pH shock in the culture tanks. It worked fine without any drip, although we tried drip for a while just because we were unsure about the shock effect. In smaller systems you can set up a bucket or barrel of whatever size, and drip it into your system at some point where it will be well mixed before being distributed to the culture system. I would have to look up the mass per gallon per pH unit in my reference book, but it is fairly easily done. You should not have to hire a consultant or resort to special products or technology.
Ted Ground <ground@thrifty.net>
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COMMENTS 3:
Are you trying to maintain a pH or actually raise it from natural seawater levels (8.3 ish)? Hydroxides will surely do the trick but it will shoot your pH up to about 12. If you are just trying to maintain normal seawater chemistry like in a loaded recirculated system sodium bicarbonate will help.
Nancy Lightowler <nlightowler@lbaop.org>
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COMMENTS 4:
I find that problems can start to develop in the marine systems when the pH falls below pH 7.8, especially in recirculation systems. Heterotrophic bacteria in the biofilters can produce acids and carbon dioxide, nitrifyers consume inorganic carbon and the fish expire carbon dioxide. The net result is a reduction in the carbonates through consumption of the carbon and displacement of the equilibrium. The balance can be restored through replacement of inorganic carbon, additional support may also be required through more active pH buffering.
If you do not have a tricking down flow biofilter, then there should be strong aeration at some part of the system. The bicarbonate may be added as a solution or as a powder directly into the system. For active pH buffering we use MagPhlow media which is composed of Magnesium hydroxide pellets. The MagPhlow media dissolves in the water in direct response to the pH of the water. At a pH of 8.3 it is insoluble, therefore it is impossible to overdose the system or cause high pH values. Also unlike calcium salts, magnesium does not form insoluble phosphates, therefore all of the MagPhlow media is available for pH buffering.
Additional information can be found on our web site at
http://www.DrydenAqua
Dr.Howard T Dryden
Dryden Aqua Ltd
Butlerfield, Bonnyrigg, Edinburgh EH19 3JQ
Scotland, UK
Tel 44(0187) 58 22222
Fax 44 (0187) 58 22229
e-mail howard@DrydenAqua.com
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web site http://www.DrydenAqua.com
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