I can confirm that the Poseidon Phytotanks definitely do work! I really like them. I have four of them running for over five years now. I do NOT use the Poseidon bags, I use "bread bags" from my local grocery store. I can get a box of 50 for less than $4. Use for one batch of phyto, then toss and use a new one. Easy, and minimal if any cleanup between batches. About once per month, I run the black rubber tops through my regular dishwasher cycle and the blue airlines through the washing machine along with the filter socks from my display tank, with bleach, then rinse x3.
I do not do the sterile technique many use, I just use my "aseptic technique" I used while working in a university microbiology lab and a tertiary hospital's blood bank.
I don't do anything special to my culture water, in fact I use my RO unit's waste water and just add IO salt and mix in a 2 gallon plastic container. Then when starting a new culture, I add my F2 and starter phytoplankton, then fill the "Phytotank" up above the rubber LED sleeve, connect to air and lighting and done for 12-14 days until it is ready for harvest.
I currently have three cultures of Nannochloropsis sp and two cultures of Chlorella sp. I have never had any luck when trying T Iso or Pavlova brown phytos, or any of the three red ones I have attempted. Perhaps those need the sterile conditions that I dont have, or my lighting, air, temp/salinity aren't agreeable, or maybe I just need to get something other than "F2". Not sure, but I am satisfied with my green phytos, they allow me to grow plenty of copepods and even hatch brine shrimp from cysts and raise them to adult size.
Here is a picture of my plankton area, a couple shelves under my basement stairs. The cultures are all at different stages of growth, I stagger them so I can harvest on a steady basis instead of all at once and then need to store somehow. Lighting is 16 on and 8 off, air pumps run 24hrs.
The two jars on the ends of the middle shelf are copepods. The bottom shelf has copepods ion the left jar, and Nanno in the right jar, which is not a phytotank, just a one gallon jar, is placed near one 10w fluorescent bulb and a 30w incandescent bulb.