YSI 6 series User Manual page 334

Chlorophyll Measurements Appendix I
Note also that your may observe less or more noise at your site with no compromise in sensor performance.
Occasional spikes during a monitoring study are normal and usually simply indicate the transient passage
of a large phytoplankton particle over the optical face during the time of sampling.
If you consistently observe periods in your monitoring study where the data is clearly unreliable due to a
large number of very high spikes, then you may have to take additional precautions to minimize the effect
(see next question).
My unattended monitoring data shows a large number of chlorophyll spikes that clearly do not
reflect the average phytoplankton content of the water. What is causing this effect and is there
anything I can do to minimize it?
This effect, shown in the initial chlorophyll readings in the figure below, can be caused by the presence of
subsurface macroscopic filamentous algae.
The flexible algal strands can become attached to the wiper arm and sometimes are resident on the probe
optics even after a cleaning cycle. The key to decreasing the spiking effect is to minimize the free algae,
which is present in the probe compartment of the sonde. This can sometimes be accomplished by encasing
the sonde guard in standard fiberglass window screen wire which is available at most hardware stores and
then anchoring the screen with rubber bands as shown in the picture below.
YSI Incorporated Environmental Monitoring Systems Operations Manual I-7