Tetraselmis is one of the most versatile live microalgae you can culture at home. Whether you're feeding Daphnia, enriching copepods, or supporting a reef tank, this complete care guide will show you exactly how to use and culture Tetraselmis successfully.
What Is Tetraselmis?
Tetraselmis is a single‑cell green phytoplankton used in aquariums as a live food, water conditioner, and microfauna booster. It’s rich in fatty acids, pigments, and nutrients that support Daphnia, scuds, copepods, shrimp, filter feeders, and reef organisms.
Aquarists use Tetraselmis for:
- feeding freshwater microfauna
- enriching live foods before feeding fish
- supporting copepod and rotifer cultures
- improving water quality in nano tanks
- feeding corals and filter feeders in marine systems
How to Use Tetraselmis in Freshwater Aquariums
Tetraselmis is marine in origin, but it is safe and effective for freshwater microfauna. It does not survive long‑term in freshwater, so it will not overgrow or cause algae blooms.
Best Uses in Freshwater
- Feeding Daphnia
- Feeding scuds (Gammarus)
- Feeding copepods
- Feeding shrimp and snails
- Conditioning live foods before feeding fish
How Much to Use
- Add enough to tint the water light green
- Feed again when the water clears
- Start small — you can always add more
How to Use Tetraselmis in Saltwater & Reef Tanks
Tetraselmis is widely used in marine systems for:
- feeding corals
- feeding filter feeders
- supporting copepod and rotifer cultures
- boosting biodiversity in refugiums
How Much to Use
- Add a small amount to lightly cloud the water
- Target feed corals with a pipette if desired
- Turn off skimmer for 20–30 minutes for best absorption
How to Store Tetraselmis
- Keep refrigerated (not frozen)
- Shake gently every few days
- Use within 4–6 weeks for best results
- If it smells foul or separates strangely, discard
How to Feed Tetraselmis to Microfauna
Daphnia
Tint water light green; feed again when clear.
Scuds
Add a small amount to cloud the water; they graze on suspended cells and biofilm.
Copepods
Excellent primary food source; use small daily feedings.
Shrimp & Snails
Provides supplemental nutrition and biofilm support.
How to Tell If You’re Feeding the Right Amount
- Water clears within 24–48 hours → perfect
- Water stays green for days → too much
- Water turns cloudy or smells bad → reduce feeding
Ready to start your own culture? Get live Tetraselmis HERE!
How to Culture Your Own Tetraselmis at Home (Simple Step‑by‑Step Guide)
Culturing Tetraselmis at home is easy, beginner‑friendly, and a great way to maintain a steady supply of live microalgae for Daphnia, scuds, copepods, shrimp, and reef tanks. This method works for both freshwater and marine hobbyists.
What You Need
- A clean, sterile bottle or jar (16–32 oz)
- Your starter Tetraselmis culture
- Clean saltwater (1.020–1.025 salinity)
- A light source (LED light or grow light)
- Fertilizer such as f2
- Gentle aeration
Step‑by‑Step Instructions
- Fill your container with clean saltwater.
- Add your starter culture (10–40% of the total volume).
- Add fertilizer (follow product instructions).
- Provide light for 12–16 hours per day.
- Add gentle aeration to keep cells suspended and oxygenated.
- Let it grow — the culture should darken over 5–10 days.
- Harvest when dark green by pouring off up to 50% of the culture.
- If your growing container looks dirty, remove remaining 50% of culture, clean and sterilize jar (optional but recommended).
- Top back up with fresh saltwater and continue the cycle.
How to Tell When Your Culture Is Ready
- Pale green → still growing
- Medium green → usable
- Dark green → ready to harvest
- Brown or clear → culture crash (restart with backup)
How Often to Split or Harvest
- Most hobbyists harvest every 5–10 days
- Never harvest more than 50% at once
- Always keep a backup bottle growing separately
Tips for Success
- Keep the culture warm (70–78°F)
- Avoid direct sunlight
- Shake gently if cells settle
- Use clean, sterile equipment to avoid contamination
- When adding new salt water, try and match temperature and salinity to reduce osmatic shock
Troubleshooting Tetraselmis Use
Water smells bad
You’re overfeeding. Reduce the amount and increase water changes.
Water stays green too long
Use smaller doses.
Daphnia or scuds aren’t responding
Feed less at a time; they may be overwhelmed.
Culture looks separated or stringy
Shake gently; if it doesn’t mix, it may be expired.
Tetraselmis FAQ — Answers to Common Questions
Is Tetraselmis safe for freshwater tanks?
Yes — it’s marine in origin but completely safe for freshwater microfauna.
Does Tetraselmis survive in freshwater?
No. It dies off naturally, making it safe and non‑invasive.
Can Tetraselmis cause algae blooms?
Not in freshwater. In saltwater, only if massively overdosed.
How often should I feed Tetraselmis?
Feed again when the water clears — usually every 1–3 days.
How long does Tetraselmis last in the fridge?
4–6 weeks when stored properly.
Can I use Tetraselmis to culture Daphnia?
Yes — it’s one of the best foods for Daphnia cultures.
Can I use Tetraselmis to feed copepods?
Yes — it’s excellent for copepod growth and reproduction.
Is Tetraselmis good for corals?
Yes — many reef keepers use it for soft corals, LPS, NPS, and filter feeders.
Can I mix Tetraselmis with Chlorella?
Yes — many aquarists use both for a broader nutrient profile.
Does Tetraselmis need to be shaken before use?
Yes — cells settle naturally; swirl gently to resuspend.
Can I overdose Tetraselmis?
Yes. Too much can cause cloudy water or oxygen drops. Start small.
Why is my Tetraselmis separating in the bottle?
It’s normal for cells to settle. Swirl gently. If it won’t mix, it may be expired.
Can I freeze Tetraselmis?
No — freezing kills the cells and ruins the culture.
Is Tetraselmis better than Chlorella?
They serve different purposes. Many aquarists use both