Phytoplankton

[Kabong]

The method I found to gage the "thickness" of my phyto is to.
Get a small container place a bread tie/clip (a red one works best) in the bottom.
Add phyto by the milliliter until you can no longer see the clip.

Of course you really need a true source to get a comparison measurement from.
I originally used some DT's to get the initial measurement.
Then grew my own and compared the difference in mm between the two.
The best batch I ever had was approx 75% concentration of DT's