Thanks a lot. Basically taking a very similar approach to you except I decided against a centrifuge as it would be quite costly for this single purpose. On the other hand I had also planned to use the centrifuge to concentrate the phyto for storage and use. Other issue was I struggled to find large enough centrifuges for concentration purposes, would be fine for water testing though.
Anyway now I’m thinking since I can’t find any reasonable chart for the cell density I might also use the color meter God built into me as well, but perhaps I’ll make a reference and measurement method to make future harvests more consistent in concentration. Something like a Salifert color test card and vial but referencing my inner color meter for the baseline. Not so scientific, I know.
Pic attached of my latest, I’m actually planning to use these bottles to seed bigger batches. I’ll be doing around 10 gallon batches. I’d like to start adding around a quart per day to my reef.
Actually I want to share my new “reactor” plan with you all but wondering where to post it

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