Table 2. Summary of the properties of the counting methods.

Method	Optimal algal concentration range a (cells ml-1 x10-3)	Required sample volume a (ml)	High-throughput capability	Operator time	Common sources of problems	Potential for human error
Hemo-cytometer	200–600	0.04	No	High	Clumps, sample volume, loading error	High
Dinofinder	10–100	0.016	No	Very High	Debris, high salt concentration, clumping	High
Coulter Counter	100–1,000 a	6	No	Moder-ately high	Incomplete homogeniza-tion, clumping	Low
Guava flow cytometer	10–500	0.1	Yes	Low	Clumps	Low

^aAt the time of counting. Note that in our standard procedure, the sample is homogenized in 500 μl and then diluted (if needed) to the optimal concentration for counting. This dilution step is not required except for samples to be counted with the Coulter Counter, for which a dilution of ~20-fold into Isoton or some comparable solution is needed. Thus, for counting with the Coulter Counter, the algal concentrations in the original homogenate must be correspondingly higher.