Quick Navigation
- What Phytoplankton Actually Is in a Reef Context
- 1. Direct Coral Nutrition and Tissue Quality
- 2. Feeding and Sustaining the Zooplankton Population
- 3. Supporting Nutrient Balance and Zooxanthellae Health
- 4. Supporting Biological Filtration and Microbial Diversity
- How to Dose Phytoplankton Effectively
- A Note from Darren
- FAQs
There are 4 ways phytoplankton impacts your reef that most reef keepers either don't know or consistently underestimate. Phytoplankton tends to get filed under "optional supplement" and deprioritised behind water chemistry, lighting, and more visible feeding tasks. That's understandable, but it underestimates what phytoplankton is actually doing in a reef system when it's present regularly.
This isn't a complicated addition to a reef keeping routine. Two or three additions per week, dosed into the sump with the skimmer off for an hour, takes a few minutes. The cumulative impact on a phytoplankton reef tank over weeks and months is consistently one of the clearest improvements reef keepers report making. Understanding the 4 ways phytoplankton impacts your reef helps you see why that improvement is predictable rather than accidental.
- Darren, Reefphyto
What Phytoplankton Actually Is in a Reef Context
Phytoplankton are microscopic single-celled algae that form the base of the marine food chain. In the ocean, they're present in the water column in enormous concentrations and every other organism in the reef ecosystem depends on them, directly or indirectly. In a home reef tank, they're almost entirely absent unless you add them. The gap between the nutritional richness of the water column in a natural reef and in a closed aquarium system is one of the fundamental challenges of reef keeping, and regular phytoplankton dosing is one of the most direct ways to close it.
Reefphyto's phytoplankton is a five-species blend, cultured fresh in Wales and dispatched live. The five-species approach matters because different phytoplankton species provide different fatty acid profiles, cell sizes, and nutrient compositions, and different organisms in your tank will preferentially absorb different species. A single-species product leaves gaps that a blend covers.
1. Direct Coral Nutrition and Tissue Quality
Corals are not passive. Many species, particularly soft corals, gorgonians, and filter-feeding invertebrates like clams and feather dusters, absorb phytoplankton directly through mucus trapping and tissue-level uptake. For these species, a phytoplankton reef tank produces measurably better polyp extension, more consistent colouration, and stronger tissue condition compared to tanks where phytoplankton is absent.
The nutritional contribution is specific. Phytoplankton provides essential fatty acids including EPA and DHA, amino acids, chlorophyll, and carotenoids that contribute to the pigmentation compounds responsible for coral colouration. It also provides the dissolved organics that all coral tissue absorbs passively as a background nutritional source, regardless of species. Even SPS corals that can't actively capture phytoplankton cells benefit from the dissolved organic contribution that phytoplankton additions maintain in the water column.
2. Feeding and Sustaining the Zooplankton Population
This is the impact that's easiest to underestimate because it's indirect, but it may be the most significant of the 4 ways phytoplankton impacts your reef over the long term. Phytoplankton is the primary food source for copepods, rotifers, and other zooplankton. Feed phytoplankton regularly, and you're feeding the organisms that feed your corals, fish, and filter feeders.
In practice, a tank receiving regular phytoplankton additions supports a higher, more stable copepod population than one that doesn't. In a refugium context, regular phytoplankton dosing feeds the copepod culture directly, extending the time between manual reseeding and increasing the density of copepod nauplii entering the display tank. For reef keepers with mandarin dragonets, pipefish, or other obligate live feeders, this indirect benefit is as important as anything phytoplankton does for the corals themselves.
The food web logic is straightforward. Phytoplankton feeds copepods. Copepods feed fish and corals. A phytoplankton reef tank that's being dosed regularly has a continuously operating food chain that a tank without it simply doesn't.
Live Zooplankton
£13.99
Live Zooplankton You've added a new coral and watched it stay closed for weeks. Your SPS aren't extending the way they should. Your fish are present and your water is clean, but the tank feels static, like something essential is… read more
3. Supporting Nutrient Balance and Zooxanthellae Health
The third of the 4 ways phytoplankton impacts your reef concerns zooxanthellae, the photosynthetic algae living within coral tissue. Zooxanthellae require trace nitrogen and phosphorus to photosynthesise efficiently. In ultra-low-nutrient systems where these elements are stripped to near-zero, zooxanthellae populations decline within coral tissue and the coral pales, not because of a lighting problem, but because its primary energy production mechanism is being starved of the building blocks it needs.
Regular phytoplankton dosing contributes a small, consistent input of organic nitrogen and phosphorus that sits at a level beneficial to zooxanthellae without pushing nitrate or phosphate into problematic ranges. This is not the same as overfeeding or allowing nutrients to accumulate. It's maintaining the trace level of biological activity in the water column that a natural reef has as a baseline and a closed aquarium system loses.
The practical outcome is corals in a phytoplankton reef tank that are photosynthesising more efficiently, showing richer pigmentation, and demonstrating better growth rates compared to corals in an identically lit but nutritionally sparse water column.
4. Supporting Biological Filtration and Microbial Diversity
A healthy reef tank is not just fish and coral in water. It's a complex microbial ecosystem in which bacteria, protozoa, and microalgae are continuously processing waste, cycling nutrients, and maintaining the chemical stability that fish and coral depend on. The fourth of the 4 ways phytoplankton impacts your reef is through this microbial layer. Phytoplankton additions support microbial diversity by providing organic carbon inputs that feed the beneficial bacterial populations underpinning biological filtration.
This contribution is background and gradual, but it's cumulative. A phytoplankton reef tank dosed consistently over months develops a richer, more stable microbial community than one running on mechanical and chemical filtration alone. The practical manifestation is better biological filtration efficiency, improved processing of ammonia and nitrite through the nitrogen cycle, and a water column that's more chemically buffered against the sudden parameter swings that stress coral.
It also contributes to what experienced reef keepers often describe as a tank that "matures" over time, developing a quality of water and inhabitant behaviour that's hard to attribute to any single factor. Consistent phytoplankton dosing is one of the consistent habits that contributes to that outcome.
How to Dose Phytoplankton Effectively
Two to three additions per week is the right cadence for most reef setups. Daily dosing is not necessary and risks overshooting the system's capacity to process the addition before it's exported. Weekly dosing is insufficient to maintain a consistently elevated food particle density in the water column.
Dose into the sump or refugium rather than the display tank directly, with the protein skimmer turned off or reduced to minimum for 60 minutes after addition. This gives corals, filter feeders, and zooplankton maximum exposure to the food before it's exported. For tanks without a sump, dose into a low-flow corner of the display and reduce wavemaker output for 30 minutes post-addition.
Start at the lower end of the recommended volume for your tank size and observe for a week before adjusting. Signs of appropriate dosing are improved polyp extension, more active copepod populations visible on the glass at night, and stable or improving water parameters. Signs of overdosing are water that stays faintly green or murky for more than a day after addition, which indicates the system's filtration isn't processing the volume efficiently.
A Note from Darren
Phytoplankton is the single most underused live food in UK reef keeping. The 4 ways phytoplankton impacts your reef all have one thing in common: their benefits accrue gradually and consistently rather than dramatically, which means they're easy to overlook when they're working and easy to dismiss when you haven't tried long enough.
If you want advice on how to integrate phytoplankton dosing into your existing routine, or which of our products suits your tank size and stocking, call us on 01267 611533 or use the contact page.
