Buy some live plankton Lfs or online get a plastic bottle say 2 litres or whatever you want to use. Put some bleach in it and warm water and wash it out then rinse 2 or 3 times with fresh water. You also need a rigid bit of plastic pipe fulll length of your bottle this needs bleached also. Put quarter of the live plankton in the bottle and three quarters salt at a salinity of 1.019 and a cap full of fertilizer I use natural seaweed . You will need a light to shine at the bottle I don’t use one I just sit it next to the window. You will see it get greener and greener as time goes on should be ready to harvest on day 12
Keep stored in the fridge
4 to 6 weeks shelf life