| The total gas meter or Tensionmeter is used for measuring the total gas
pressure in water which includes; the concentration of nitrogen, oxygen, argon and carbon
dioxide etc. Gas bubble trauma and sub-lethal toxicological problems can be caused by
total gas pressure over 100%, even levels in the order of 100.5% have been known to cause
chronic problems. There are many reasons for the development of gas supersaturation such
as increasing water temperature, turbulent injection of air in falling water, pressurized
pumping and sometimes in well or spring water. Algal blooms in freshwater and sea-water
can also cause supersaturation with oxygen. The tensionmeter provides a quick and accurate
measurement of the dissolved gas pressure. |
Fish Mortalities from gas pressure of
102 to 103% total gas pressure. |
| Although Gas Bubble Disease was rather well described eighty years ago in 1907 by
Marsh & Gorham the problem was not well known to fish culturists and was often
"rediscovered" as facilities were expanded, built in new locations, or otherwise
altered through man made or natural causes. More recently, increases in "accelerated
aquaculture" involving pumped water, extra aeration and hyperoxygenation has also led
to severe outbreaks in numerous cases. Recognition in the late 1960's that the entire
Columbia River in the Northwest USA was supersaturated to levels lethal to downstream
migrant salmon, focused an unprecedented amount of attention on the recognition,
pathology, analysis and avoidance of this condition. In like manner the current interest
in supplemental oxygen addition for purposes of restoring water quality and/or increased
production of fish per volume of water has prompted development of reliable and consistent
techniques for monitoring all relevant parameters.
The chief hazard in all systems for enhancing oxygen concentration is that the
total gas pressure, (TDGP) may exceed atmospheric plus hydrostatic pressure(due to the
depth of the water column), due to the lack of provision for removing enough of the extra
nitrogen in the water source to make up for the extra oxygen added. In many situations
therefore it is desirable if not necessary to monitor both oxygen and TGDP(Pt) or percent
saturation relative to atmospheric pressure. In most cases however a simple measurement of
% saturation available from the ToGa will indicate if the supersaturation is over 100% and
therefore of concern.
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