The phyto settles to the bottom of the container, it's the sludge you see at the bottom of the container when it sits for a day or so. Thats the actual phytoplankton, the water left above is just that, water. If you leave it long enough, you will have a thick green sludge, and clear water at the top.
It should be shaken/inverted a couple times once day to keep the phyto in suspension.
FWIW, I used to dose that weak sauce from algae barn. I have found better products and at much better prices from members on these forums. Just do a search for
@Eldredge , his phyto compared to algae barns is no comparison. Much darker/denser, 8 species blend, and it's shipped fresh every Tuesday in priority 3 day shipping.