Phytoplankton is the foundation of every live food chain in reef tanks. It feeds copepods, rotifers, clams, corals, and filter feeders. Culturing your own is cheap, simple, and sustainable.
For beginners, Nannochloropsis is the hardiest and easiest strain to start with.
What you'll need
- A super-clean, sterilised culture container (5 to 20 L is common). Cylindrical, rectangular, hexagon, doesn't matter. Something that holds a decent volume of water is all you're after.
- RODI saltwater at 1.018 to 1.023 salinity
- A bottle of healthy live phytoplankton
- Fertiliser (Guillard's F/2 is the standard)
- Light source (6,500K or a grow light)
- Gentle aeration (rigid tube and airline tubing)
- Patience. Not all cultures will succeed, so keep 100 to 200 mL in the fridge as backup for the inevitable crash.
Steps
Fill your container. Use clean saltwater. Add fertiliser as directed.
Add phytoplankton. Pour in your starter culture.
Aerate and light it up. Continuous aeration keeps the cells suspended. Light it 16 to 24 hours per day. A cheap LED or strong indirect sunlight works fine.
Wait and watch. Over 5 to 7 days, the water will darken. That's your phytoplankton multiplying. Don't let it grow too dense, since cell shading, nutrient depletion, and cell lysis (death) all start to set in once the culture peaks.
Harvest and feed. Once it reaches a rich dark green, pour off what you need (through a sieve if you're feeding pods). Clean your culture container and start the next cycle.
Maintain or split. Split cultures weekly to avoid crashes.
Tips
- Phytoplankton needs serious movement. Make sure your aeration is strong enough to agitate the surface noticeably, not just dribble bubbles.
- Run different strains in parallel for broader nutrition when you blend at feeding time.
- Always clean your culture container between harvests. Never top up an existing culture.
