How to Culture Phytoplankton at Home
You can culture live Nannochloropsis phytoplankton at home with a clean vessel, freshly mixed saltwater, steady aeration, suitable culture nutrient and a consistent light cycle. The key is cleanliness: contamination and late harvesting cause more failures than complicated equipment.
- Start with a fresh, live Nannochloropsis culture rather than preserved coral food.
- Use newly mixed saltwater at about 1.020 specific gravity—never aquarium water from the display.
- Keep the culture moving with steady bubbles and use a regular light-dark cycle.
- Harvest while the culture is dense green and still smells clean, then restart it with fresh medium.
- Keep a second culture as backup because even a well-run batch can crash.
What you need to culture phytoplankton
For a basic home setup:
- Live Nannochloropsis phytoplankton to seed the culture
- One or preferably two clear culture vessels
- Air pump, airline and rigid tube
- Light with a timer
- Freshly mixed saltwater
- Refractometer or reliable salinity meter
- Microalgae culture nutrient suitable for Nannochloropsis
- Clean measuring equipment
- Separate bottles for harvested phytoplankton
- Unscented sanitising method suitable for culture equipment, followed by thorough rinsing and complete neutralisation where required
Do not start with display-tank water. It can introduce bacteria, copepods, rotifers and competing algae that consume or overtake the phytoplankton.
Choosing a starter culture
Live Phytoplankton from Krakking Korals contains live Nannochloropsis and is available in 250 ml, 500 ml and 1,000 ml bottles. Use a fresh bottle as the starter and keep enough aside in the fridge as insurance until the new culture is clearly growing.
A starter must be live. Shelf-stable blends and preserved coral foods can feed a reef, but they will not establish a living culture.
Simple bottle setup or dedicated reactor?
A clear bottle is enough for a small culture. Use two vessels if possible so one contamination event does not wipe out the entire supply.
For a larger, tidier setup, the Aqua Medic Plankton Light Reactor II provides a roughly 5-litre chamber, integrated 10 W LED, air and carbon-dioxide connections, and a drain hose for partial harvesting. Normal home requirements do not need additional carbon dioxide; steady aeration is the practical starting point.
How to culture Nannochloropsis step by step
1. Clean the culture equipment
Clean and sanitise the vessel, airline, rigid tube, lid and measuring tools before every restart. Rinse thoroughly and ensure no sanitiser remains.
Keep phytoplankton equipment separate from aquarium maintenance gear. A net, turkey baster or airline used in the reef can carry grazers into the culture.
2. Mix fresh saltwater
Prepare new saltwater with purified water and marine salt. A practical starting point for Nannochloropsis is around 1.020 specific gravity. Match the starter culture when its supplier gives a different target.
Do not use old water-change water. It contains organisms and dissolved material that make the culture less predictable.
3. Add the culture nutrient
Nannochloropsis needs more than light and saltwater. Reef Revolution F/2 Algae Fertiliser A + B supplies the major and minor trace elements, nutrients and vitamins needed for healthy microalgae growth. You need both Part A and Part B; use them together at the measured dose on the product label.
Do not improvise with garden fertiliser or pour unmeasured aquarium supplements into the culture. The aim is a repeatable food culture, not simply green water.
4. Add the live starter
Pour the live Nannochloropsis into the prepared culture medium using clean equipment. Starting with a visibly green culture gives it a better head start than stretching a small starter across a very large volume.
Keep a backup portion refrigerated until the first batch has darkened and survived its first split.
5. Add steady aeration
Run rigid airline close to the bottom of the vessel so the whole culture stays moving. Aim for a steady stream of bubbles that keeps cells suspended without producing heavy foam.
Do not use an airstone if it is hard to clean or causes persistent foam. Simple open-ended rigid airline is easier to inspect and sanitise.
6. Set a consistent light cycle
Place the light close enough to illuminate the full culture without heating it. Start with roughly 14–16 hours of light and 8–10 hours of darkness each day.
Consistency matters more than running the light continuously. If the vessel becomes warm, move the light farther away or improve ventilation rather than accepting a temperature swing.
7. Watch the colour and smell
A healthy Nannochloropsis culture should become progressively darker green as cell density rises. It should remain evenly suspended while the air is running and smell fresh or mildly marine.
Check it daily. A sudden colour loss, clumps, surface film, bad smell or visible small animals suggests contamination or a crash.
8. Harvest before the culture declines
Many home cultures are ready to split in roughly 7–10 days, but colour and growth rate matter more than the calendar. Harvest while the batch is dense green and still actively growing.
Remove a portion for feeding or refrigeration. Leave enough healthy culture to restart the next batch, then top up with fresh, sanitised saltwater medium and the measured culture nutrient.
Do not keep topping up one vessel indefinitely. Regular cleaning and full restarts reduce the buildup of contaminants.
A practical two-culture routine
Run two smaller cultures a few days apart rather than one large batch. Harvest Culture A while Culture B remains untouched. At the next split, reverse them.
This gives you a backup if one bottle crashes and prevents you from feeding the entire mature culture to the tank by mistake.
Label every bottle with the strain and split date. Use separate airline and pouring equipment for each culture where possible.
How to store harvested phytoplankton
Transfer harvested phytoplankton into a clean bottle and refrigerate it promptly. Gently shake the bottle every few days to keep the cells suspended.
Never pour unused phytoplankton from a feeding cup back into the storage bottle. Aquarium water introduced by a syringe, pipette or cup can contaminate the whole batch.
Krakking Korals' feeding guidance for its live Nannochloropsis is 10–20 ml per 100 litres every second day. Start conservatively and watch nutrients and livestock response because every reef has a different stocking and filtration load.
How to tell if the culture has crashed
Discard the batch if you see any of these warning signs:
- Green colour fades rapidly instead of deepening
- Rotten, sulphurous or sharply unpleasant smell
- Heavy clumping, slime or persistent surface film
- Culture clears while tiny grazers become visible
- Sediment builds quickly and does not resuspend
- The batch stops darkening after conditions were previously stable
Do not dose a questionable culture into the reef. Clean and sanitise the equipment, then restart from the refrigerated backup or a new bottle of live culture.
Common phytoplankton culture mistakes
- Using display-tank water: this imports competitors and grazers.
- Starting with preserved phytoplankton: non-living food cannot reproduce.
- Skipping culture nutrient: light alone does not provide nitrogen, phosphorus and trace nutrients needed for growth.
- Overheating with the light: a warm vessel can crash quickly even when the room feels cool.
- Weak aeration: settled cells receive uneven light and gas exchange.
- Harvesting too late: an ageing culture can exhaust its nutrients and collapse.
- Running only one vessel: one contamination event removes the entire supply.
- Sharing tools between cultures: cross-contamination defeats the backup system.
- Returning feeding leftovers: this introduces aquarium organisms into stored phyto.
FAQ
Can bottled live phytoplankton start a culture?
Yes, provided it contains living cells and is still fresh. Krakking Korals' live product contains Nannochloropsis, which is commonly used as a hardy starter strain.
Can I culture phytoplankton with aquarium water?
Do not use display-tank water. Prepare fresh saltwater because tank water can carry bacteria, copepods, rotifers and competing algae into the culture.
Does phytoplankton need fertiliser?
It needs a measured microalgae culture nutrient suitable for the strain. Light and saltwater alone will not sustain repeated dense harvests.
How long does a phytoplankton culture take?
A healthy home batch often becomes ready to split in about 7–10 days, but use colour, smell and active growth rather than the calendar alone.
Should phytoplankton have light 24 hours a day?
A regular light-dark cycle is the safer starting point. Roughly 14–16 hours of light gives useful growth while limiting heat and allowing a dark period.
Why did my phytoplankton turn clear?
The likely causes are contamination by grazers, exhausted nutrients, heat, weak aeration or harvesting too late. Discard a bad-smelling or questionable batch and restart with clean equipment.
Can I grow phytoplankton and copepods in the same bottle?
Not if the goal is to maintain a dense phytoplankton culture. Copepods graze on the algae and can clear it. Keep production cultures separate and use harvested phyto to feed the pod culture.
The reliable method
Keep it clean, keep it moving, split it while it is healthy and always maintain a backup. Once that routine is stable, a home Nannochloropsis culture becomes a repeatable source of live food for copepods and suitable filter feeders rather than a bottle you need to replace each week.