If water samples are taken, the in vivo data can be correlated to extracted chlorophyll a data to estimate actual concentrations. Otherwise, the in vivo data can be used as a relative measurement to identify trends and patterns. This step may not be necessary in some systems and tests should be run to compare extractions with and without grinding. Non-grinding techniques can use either GFF or membrane filters that will dissolve in the solvent. Light, temperature, water quality, and dissolved components can all have significant effects on fluorescent readings independent of the chlorophyll concentration.
Temperature has an inverse relationship with fluorescence.
For example, in a vertical profile, as the temperature decreases, the fluorescence will increase independent of chlorophyll concentration. Turner Designs' field and submersible instruments have the capability to automatically compensate for temperature effects. Light history can have significant affects on the fluorescence in algal cells. For example, at low light levels, algal cells can optimize the light uptake by pushing chloroplasts to the outer edge of the cell or by producing more chlorophyll per cell. Both of these responses can result in data increases the fluorescence signal while the algal biomass may be unchanged.