I culture my own phytoplankton. I have done nanochloropsis, Isocrysis, and tetraselmis for different sizes. My honest opinion is it is more trouble than it is worth but after 5 months I have a good system down. I did six 2L bottles when I started but I now only do three 2L bottles for my 360 gallon system. I culture it for 2 weeks then place in my fridge. After 2-3 days of settling I dump the cleanish water slowly from the storage bottle making sure to keep my phytoplankton in the bottom. Then I have a fairly dense mixture I can put in a smaller storage bottle. I put some in every other day.
I buy from Florida Aqua Farms to get my culture and my micro-algae grow nutrients.
If you ever make it to Huntsville I can get you a sample from my system to start your culture and some nutrients. Actually, I may have an extra culture disk I could sell you and possibly even ship if you wanted.