Marine Phytoplankton Dosing Guide for Reefs
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A bottle of live phyto is not a substitute for a feeding plan. In a stable reef, marine phytoplankton dosing is a controlled way to supply suspended nutrition to filter feeders, support copepod reproduction, and reinforce the microfauna that turns a glass box into a functioning food web. The right dose is the amount your system consumes without leaving excess nutrients, haze, or waste behind.
That number is not identical for every aquarium. Tank volume matters, but livestock density, filtration, feeding frequency, and the density of the live culture matter just as much. A lightly stocked SPS system with a strong skimmer will respond differently than a refugium-heavy mixed reef, a clam display, or a dedicated copepod culture. Start conservatively, measure the response, and adjust one variable at a time.
What Live Phytoplankton Is Doing in Your System
Marine phytoplankton is food at the base of the aquatic food chain. Different microalgae have different cell sizes, fatty-acid profiles, pigments, and digestibility. That is why color alone is not a dosing instruction. Green, gold, and red phytoplankton categories can serve different feeding roles, but performance depends on the actual species, culture condition, and cell density.
In reef aquariums, live phyto is commonly used to feed copepods and other zooplankton, supplement nutrition for filter-feeding invertebrates, and maintain a productive refugium or cryptic-zone community. It may also support animals such as clams, feather dusters, sponges, and certain corals that capture fine suspended particles. It is not a cure for poor coral nutrition, unstable alkalinity, inadequate flow, or declining water quality.
A live, actively feeding culture has an operational advantage over tinted water with uncertain cell counts: you are adding viable cells rather than relying on color as proof of nutrition. PodDrop cultures are produced in isolated, controlled systems so reef keepers can dose with greater confidence in purity and culture performance. Still, every aquarium determines the final dosing rate.
Marine Phytoplankton Dosing Guide: Start With a Baseline
For a dense live phytoplankton culture, a practical starting range is 5 mL per 10 gallons of actual system water per day. Actual water volume means water after accounting for rock, sand, equipment, and sump operating level. A nominal 100-gallon aquarium may hold substantially less than 100 gallons of water.
Run that starting dose for seven days before making a meaningful adjustment. If the system has a large refugium, a visible copepod population, clams, sponges, or a heavy filter-feeder load, increase gradually toward 10 mL per 10 gallons per day. For a new system, an ultra-low-nutrient SPS aquarium, or any tank already fighting elevated nitrate or phosphate, begin at half the baseline dose.
This guide assumes a high-density live product. Always defer to the specific product label when its recommended rate differs, because 5 mL of one culture can contain a very different number of cells than 5 mL of another. Dosing by volume only works when the culture density is consistent.
Use a Ramp, Not a Large First Dose
A large initial dose can cloud your read on cause and effect. If nitrate rises, phosphate climbs, or the water becomes persistently hazy, you need to know whether phyto was the driver or whether the system was already accumulating excess organics.
Use this simple progression when introducing phytoplankton:
- Days 1-7: Dose 5 mL per 10 gallons daily, or 2.5 mL per 10 gallons in nutrient-sensitive systems.
- Days 8-14: Increase by 25% to 50% only if livestock response is positive and nutrient trends remain stable.
- Week 3 onward: Hold the lowest dose that sustains the desired result, whether that is stronger pod activity, improved filter-feeder extension, or more consistent refugium production.
- If nutrients or haze increase: Reduce the dose by 25% to 50% and hold there for a full week before changing it again.
When to Dose Phytoplankton
Daily dosing usually produces the most stable food availability. Small, repeated additions better match how natural plankton enters reef environments and avoid a single heavy pulse of nutrients. If daily manual dosing is not practical, dose every other day at roughly twice the daily amount, then observe the same water-quality markers.
Many reef keepers dose after lights out or shortly before the main display lights dim. This can be useful because copepods and other microfauna often become more active during lower light periods. It also allows the culture to circulate before aggressive daytime feeding activity resumes. However, timing is secondary to consistency. A dose delivered at the same reliable time each day is more useful than an ideal schedule that is rarely followed.
Do not shut down all circulation. Phytoplankton needs to disperse throughout the display, sump, and refugium. Keep return flow and powerheads operating. If you run a protein skimmer, you can either leave it on or pause it briefly for 30 to 60 minutes. Leaving it on favors stability and oxygen exchange. Pausing it may increase contact time with filter feeders. The better choice depends on how close your system already runs to its nutrient and oxygen limits.
Dose for the Goal, Not the Bottle
The correct target changes with the reason you are feeding.
For Copepod Population Support
Copepods need a dependable food source, particularly when establishing a new population or maintaining pod-dependent fish such as mandarins and dragonets. Dose lightly but consistently, with special attention to the refugium, rockwork, and other protected habitat. Phyto supports the food web, but it cannot compensate for a lack of habitat or excessive predation.
If pod numbers are falling despite regular phytoplankton feeding, examine mechanical filtration, refugium design, fish pressure, and whether the original copepod addition contained a viable, appropriately sized population for the system. Adding more phyto to an unsuitable environment usually adds nutrients before it adds pods.
For Filter Feeders and Clams
Filter-feeding livestock benefits most from frequent, modest suspended feeding. Target feeding may be appropriate for specific animals, but broadcast dosing is generally the more practical method for maintaining background food availability across a mature reef. Watch for feeding behavior, tissue condition, and water clarity rather than expecting an overnight visual change.
For Coral-Dominant Reefs
Phytoplankton is not a complete coral feeding program. Most photosynthetic corals rely heavily on light and dissolved or particulate nutrients obtained through several pathways. In coral-dominant systems, phyto is best treated as a food-web input that supports microfauna and fine-particle feeders, not as the sole route to color or growth.
Measure the Response That Matters
Test nitrate and phosphate at least weekly while changing your dose. The goal is not necessarily zero nutrients. Many productive reefs perform well with measurable nutrients, but the acceptable range is specific to the livestock, lighting, export capacity, and feeding load. What matters is whether values are stable and intentional.
Also look beyond test results. Positive signs include visible copepods in refugium zones and on glass after dark, consistent polyp behavior, healthy filter-feeder extension, and clear water with no accumulating film. Warning signs include persistent water cloudiness, cyanobacteria or nuisance algae gaining ground, a rising nutrient trend without another explanation, or detritus building in low-flow areas.
Do not interpret one observation as proof. Coral extension can change with flow, lighting, fish activity, and feeding. Nitrate can move after a change in fish food, skimmer performance, or maintenance habits. Track your dose and test results for at least two weeks so adjustments are based on a trend rather than a single data point.
Storage and Handling Affect the Dose You Deliver
Live phytoplankton is perishable. Refrigerate it promptly according to the culture instructions, keep the cap closed between uses, and avoid freezing or overheating the bottle. Gently invert or swirl before dosing so cells are evenly distributed. Do not shake aggressively enough to create excessive foam.
Use clean measuring tools. Introducing tank water or contaminated equipment into the bottle can shorten culture quality and compromise a product that began as a clean, single-species culture. Pour out only what you plan to use, and never return excess liquid to the container.
A dosing pump can improve consistency, but verify that its tubing and pump head are compatible with live culture handling and clean them on a schedule. For smaller tanks, manual dosing with a graduated syringe is often more accurate and easier to audit.
The best phytoplankton program is deliberately uneventful: stable nutrients, a clear system, active microfauna, and livestock receiving a consistent baseline of live nutrition. Start lower than your instinct tells you, let your measurements lead, and increase only when the aquarium demonstrates it can use more.