Subject: How can I measure phytoplankton concentration in water?

I want to examine the response of the rate of growth of phytoplankton in water
to different environmental parameters. I need an inexpensive way to measure the
concentration of blue green algae in water samples. I can't destroy the water
samples (or much of it) to make the measurement. Is there an inexpensive
spectrometer or other instrument that makes such a measurement, and where can I
get one (or use one)? Thank you.

Re: How can I measure phytoplankton concentration in water?