YSI YSI 556 MPS, Set-Up, Operation & Calibration

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Dissolved Oxygen
For best results, we recommend that the KCl solution and the membrane cap be
changed at least once every 30 days.
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The rate of stirring should be at least 1 foot per second.
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Membrane life depends on usage. Erratic readings are a result of loose, wrinkled,
damaged, or fouled membranes, or from large (more than 1/8" diameter) bubbles in
the electrolyte reservoir. The average replacement interval is two to four weeks.
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If the membrane is coated with oxygen consuming (e.g. bacteria) or oxygen
producing organisms (e.g. algae), erroneous readings may occur.
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Chlorine, sulfur dioxide, nitric oxide, and nitrous oxide can affect readings by
behaving like oxygen at the sensor. If you suspect erroneous readings, it may be
necessary to determine if these gases are the cause.
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Avoid any environment that contains substances that may attack the probe module
and sensor materials. Some of these substances are concentrated acids, caustics,
and strong solvents. The sensor materials that come in contact with the sample
include FEP Teflon, acrylic plastic, EPR rubber, stainless steel, epoxy,
polyetherimide and the PVC cable covering.