Hello Marius,

When i need to count motile green algae such as Dunaliella or Tetraselmis i use a diluted solution of iodine tincture, just few drops in your sample, but don't exceed or you will have a too bright color.

Otherwise you can prepare the classic lugol solution or a 5% formaldehyde solution

If you don't need the cells back, then the same can be treated with very dilute Formaldehyde.

An alternate way is to first make a solution of Menthol in seawater separately (the chemical takes a bit longer to dissolve) & with a micropipette, add very small drop/s of the solution on the observation/counting slide. Within a short time, the cells will get immobilized.

Thanks alot! I tried the 5% formaldehyde option and it certainly worked well.

Lugol's solution works well for me. It makes the cells heavier than water, so they sink. Apply to 0.4%. Cells will change colour, but they won't lose their flagella.