Multi-Strain/Mix Phyto: Great for Feeding; Bad for Culturing
Phytoplankton is the foundation of many marine systems; vital for reef tanks, aquaculture, and breeding setups. Whether you're feeding copepods, rotifers, corals, filter feeders, or other little creatures, multi-strain phytoplankton offers a nutrient-rich, well-rounded option. But while it’s excellent for feeding, attempting to culture it long-term almost always results in one strain taking over.
Whether 2-strain, 3-strain, or 30-strain, it’s important to know what each species contributes; and why mixed cultures don’t stay balanced over time.
Why Multi-Strain Phyto Is Ideal for Feeding
In the ocean, nothing feeds on just one species of plankton. Diversity in size, nutritional content, and movement is part of what makes natural systems so robust. Multi-strain mixes try to replicate this by combining strains like Nannochloropsis, Isochrysis, and Tetraselmis.
Here’s what you gain:
Better nutrition; Each strain offers something different: Isochrysis is rich in DHA, Nannochloropsis is high in EPA, and Tetraselmis offers a broader mix of proteins and sugars.
Wider appeal; Different organisms prefer different food sources. A blend ensures coverage for copepods, clams, sponges, corals, and other little creatures.
Improved tank resilience; A mix increases the odds that at least one strain will remain active in fluctuating conditions (light, flow, nutrient swings).
Convenience; A single bottle with multiple strains saves time and dosing effort while still feeding a wide range of livestock.
However, it’s important to note that multi-strain blends don’t store as well as single-strain cultures. Even when mixed fresh at the time of shipping, shelf life is significantly reduced. Sensitive strains like Isochrysis may start to die off within days if not refrigerated properly or exposed to heat during transit. By the time the bottle arrives, what was a 3- or 4-strain blend could be mostly Nannochloropsis; with no visual cues that anything has changed.
For feeding purposes, multi-strain phyto is still a smart option; just understand that freshness and cold-chain handling are critical to preserving the full blend.
Why It Fails in Culture
Despite being great for feeding, trying to propagate a mixed phytoplankton culture rarely works long-term.
Why?
One strain always wins; Fast growers like Nannochloropsis outpace slower strains like Isochrysis. Over time, they consume most of the nutrients and take over.
Different needs; Each strain thrives under different light, salinity, and nutrient conditions. In one shared environment, you're always favoring some and suppressing others.
Invisible dominance; Just because the culture stays green doesn’t mean it’s still a balanced mix. Often, only one strain remains viable.
No way to reverse it; Once one strain has taken over, you can’t just “re-balance” the culture. You have to start fresh with pure, isolated strains again.
This can be true even before you try to culture it. Many blends arrive with only one viable strain left, especially if exposed to warm temperatures during shipping. The bottle might say "multi-strain", but by the time you open it, it could already be a monoculture; meaning your starting point is flawed without you even knowing.
This happens regardless of how carefully the original blend was prepared; shelf life is simply shorter with mixed strains, and survivability varies too much between species.
Best Practice: Blend at Feeding Time
If you want both control and diversity:
Maintain separate single-strain cultures; This gives you full control over each strain’s growth and health.
Mix them only when feeding; Combine the desired strains in a separate container, just before dosing.
This way you keep nutritional variety, avoid competition issues, and always know exactly what’s going into your tank.
It also lets you adjust the blend based on what you're feeding; whether that’s copepods, larvae, or filter feeders like clams, corals, or other little creatures.
Plus, by keeping strains separate until use, you bypass the shelf life issue entirely. Each single-strain culture can be maintained fresh and alive, and you won’t risk receiving a bottle where only one strain has survived the trip.
Final Word
Multi-strain phytoplankton is excellent for feeding; but not for culturing. If you try to grow it long-term, the diversity that made it valuable will collapse into a single surviving strain.
To keep your system thriving and your dosing consistent, culture each strain individually and blend only when needed. You’ll get reliable results and all the benefits of variety; without the slow fade into monoculture—or the surprise of a dead-on-arrival blend.
