FREQUENTLY ASKED QUESTIONS
Hydralife Greenwater FAQ
Green water is water rich in live, suspended microscopic green algae (phytoplankton), used as live food and as a culture medium for zooplankton and fish fry. Hydralife Greenwater is live, multi-species freshwater phytoplankton by Hydralife Solutions, Denver, Colorado, used to feed daphnia, moina, copepods, rotifers and fish fry and to inoculate outdoor ponds. It ships alive in 32 oz breather bags to the lower 48 states, Monday through Thursday.
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Answers kept by Hydralife Solutions. Last updated October 2026.
5 QUESTIONS
What Greenwater Is
What is green water?
Green water is water rich in live, suspended microscopic green algae (phytoplankton), which give it its green color. It is used as live food and as a culture medium for zooplankton such as daphnia, moina, copepods and rotifers, and for fish fry. The color comes from the chlorophyll in the living cells. In aquaculture the same idea is called the green water technique: live microalgae are added straight to larval rearing tanks. Feed-grade green water is grown on purpose; it is not the same thing as an unplanned bloom in a display tank.
Source: FAO, Manual on the Production and Use of Live Food for Aquaculture, 1996.
What is Hydralife Greenwater?
Hydralife Greenwater is live, multi-species freshwater phytoplankton by Hydralife Solutions, Denver, Colorado, used to feed daphnia, moina, copepods, rotifers and fish fry and to inoculate outdoor ponds. Hydralife grows each species in its own closed photobioreactor with controlled nutrients, minerals and lighting, then blends them at harvest. Each order is cultivated for you and shipped alive in 32 oz breather bags, ready to pour. It is a feed organism, eaten alive by the zooplankton and fry that in turn feed your fish.
Is Greenwater the same as the green water that clouds an aquarium?
No. Greenwater is grown on purpose as live food, while green water in a display aquarium is an unplanned bloom fed by excess nutrients and light. Greenwater belongs in culture vessels, fry-rearing tanks and outdoor ponds. It is not intended for indoor display aquariums, where the phytoplankton can bloom and tint the water depending on your lighting and nutrient load.
What species of phytoplankton are in Greenwater?
Greenwater is a blend of multiple freshwater phytoplankton species, each grown in its own monospecific closed system and blended at harvest. Each species was selected for its nutritional value to zooplankton, fish fry and minnows, and together they span a range of cell sizes, from the smallest that rotifers and newly hatched fry can handle up to what adult daphnia and copepods filter. The species in the blend are proprietary. If you are looking for a specific species for your culture, contact us directly.
Is Greenwater freshwater or marine phytoplankton?
Greenwater is freshwater phytoplankton, grown in fresh water for freshwater cultures. Many bottled phytoplankton products in the aquarium trade are marine, grown in saltwater for reef tanks. Daphnia, moina and most freshwater copepods and rotifers live in fresh water, so Greenwater is made for them.
5 QUESTIONS
Feeding Daphnia, Moina, Copepods and Rotifers
How do I feed Greenwater to daphnia and moina?
Pour Greenwater straight into your daphnia or moina culture after matching its temperature. For maintenance feeding, add enough to keep the culture water visibly green, then feed again when it clears. For a new culture, use Greenwater as the base water before adding your starter colony. There is nothing to mix or measure.
How much Greenwater should I feed, and how often?
Feed enough to tint the culture water visibly green, and feed again when the water clears. Clear water is the sign a moina or daphnia culture is running out of food. For reference, aquaculture guidance puts the ideal algae density for daphnia culture at about 100,000 to 1,000,000 cells per milliliter. Fry tanks use less volume but need it more often. Tell us your setup and we will size it with you rather than have you guess.
Source: FAO, 1996; Rottmann et al., UF/IFAS EDIS CIR1054.
How do I know if my culture is underfed or overfed?
Clear water and pale animals with empty guts mean a culture is underfed; fouled water and fungal growth mean it is overfed. Underfed moina also start producing resting eggs, a stress response. Overfeeding raises ammonia, and daphnia need ammonia kept below 0.2 mg per liter. Because Greenwater is alive, uneaten cells keep living in the water instead of rotting the way leftover powder does.
Source: Rottmann et al., UF/IFAS EDIS CIR1054; FAO, 1996.
Can I feed Greenwater to copepods and rotifers?
Yes. Copepods and rotifers feed on live phytoplankton, and a steady, dense supply keeps those cultures producing. The best food size for the freshwater rotifer Brachionus calyciflorus is roughly 3.5 to 10 micrometers, and the Greenwater blend spans small cell sizes so rotifers, copepod nauplii and adults all find food they can capture. Buying Greenwater means you do not have to run a separate algae culture alongside your copepods or rotifers.
Source: Drago et al., Frontiers in Environmental Science, 2020.
Should Greenwater go in the same container as my daphnia?
Yes, feed Greenwater straight into the culture, and keep any Greenwater you are not using yet in a separate container. Store that reserve with light aeration and a strong light source, or in the refrigerator, and add it as the culture water clears. Keeping the reserve separate stops a fast-growing colony from grazing all of it at once.
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Fish Fry
Can I use Greenwater for fish fry?
Yes. Greenwater supports fry rearing, especially for small-fry species such as bettas, gouramis, killifish, rainbowfish, sunfish, bluegills and egg-scatterers. Many newly hatched fry eat the tiny live prey that graze on phytoplankton, such as rotifers and young moina, and some take the algae cells directly. The cells stay suspended where fry feed and do not break down and foul a rearing vessel the way dry foods do.
Source: FAO, 1996.
Why do fish breeders add green water to fry tanks?
Fish breeders add green water to fry tanks because it helps larvae find food and steadies water quality. In larval rearing, green water is thought to raise feeding by improving visual contrast and light dispersion, stabilize water quality in static tanks, and keep live prey nutritious while it waits to be eaten. Researchers say these effects are not fully understood, and one study on larval cod found no effect on first feeding. Keep light aeration on, because algae use oxygen at night, and watch pH, since a heavy bloom can push it above 9.5.
Source: FAO, 1996; Seafish, 2006; Rottmann et al., UF/IFAS EDIS CIR1054.
5 QUESTIONS
The Science
Is live Greenwater better than yeast, spirulina powder or dried food?
Yes for culture health: live algae are digested better and do not foul the water the way yeast and powders do. Yeast is poorly digested by many filter feeders and needs bacteria to break it down, which is a known cause of crashed rotifer cultures. Dry feeds settle, clump and leach nutrients into the water. In one study, the rotifer Brachionus calyciflorus peaked at about 103 per milliliter on Chlorella against about 57 to 62 on yeast, and a daphnia study found diets need at least 25 percent live algae to keep the animals in good condition.
Source: FAO, 1996; Sarma et al., Revista de Biologia Tropical, 2001; Michels and De Meester, 1998.
Can daphnia and moina eat cells this small?
Yes. Daphnia filter so finely that they can take up particles as small as bacteria, about 1 micrometer. Measured filter mesh openings in four daphnia species were about 0.4 to 0.7 micrometers. Daphnia also select: long, thin or filamentous cells are harder for them to handle than small round ones. The Greenwater blend is made of small single cells, which is the shape filter feeders handle best.
Source: FAO, 1996; Gophen and Geller, Oecologia, 1984; Hartmann and Kunkel, Hydrobiologia, 1991.
How nutritious is Greenwater for zooplankton?
The species in Hydralife's blend are among the most nutritious natural feeds in freshwater aquaculture. Two of our species run 50 to 60 percent protein by dry weight, among the most protein-rich organisms known, while our other species typically carry 40 to 50 percent. All of them produce polyunsaturated fatty acids, including the omega-3 and omega-6 fats that zooplankton like daphnia cannot synthesize themselves and must obtain from their diet, and one of our species is a particularly strong source of EPA. The blend also delivers B-complex vitamins, vitamin E, carotenoids such as beta-carotene and astaxanthin, and essential minerals including iron, calcium, magnesium and zinc, which support zooplankton metabolism, shell formation in daphnids and copepods, and reproductive success. Cell size and digestibility matter as much as the nutrition inside. The blend spans a range of small cell sizes with no toxic secondary metabolites, so everything from rotifers and copepod nauplii up to adult daphnia can capture and digest it efficiently. Another of our species stays suspended in the water column, where filter feeders work. That combination is why Greenwater keeps daphnia, moina, copepod and rotifer cultures well fed.
Why does a multi-species blend matter?
A multi-species blend gives zooplankton and fry a broader diet than any single alga. Food quality differs between algae: in one study, daphnia grew on green algae such as Chlamydomonas and Scenedesmus, but cryptomonads carried far more of the long-chain omega-3s. Different zooplankton and life stages also take different cell sizes. Hydralife grows each species separately and blends them at harvest so one bag covers more of those needs.
Source: Ahlgren et al., Journal of Plankton Research, 1990.
Why do homemade green water cultures crash?
Homemade green water cultures crash when light, nutrients, temperature, pH or contamination slip out of range. Growth slows below about 61°F (16°C), many species do not survive above about 95°F (35°C), and most do best at pH 7 to 9. Near pH 10 some nutrients precipitate and a culture can collapse completely. Bacteria, rotifers and competing algae can take a culture down in days, and rebuilding costs two to three weeks while your zooplankton go hungry.
Source: FAO, 1996; Creswell, SRAC 5004, 2010.
2 QUESTIONS
Using Greenwater
What should I do when my Greenwater arrives?
Use it the day it arrives for the densest, most active cells. Float the bag in your destination water for about 30 minutes if the temperatures differ, then add the whole bag to your culture or pond. In an outdoor pond, pour it into the water column. If you cannot use it all at once, see the storage answer below.
Can I use Greenwater in my outdoor pond?
Yes. In a pond the phytoplankton absorbs excess nitrogen and phosphate, uses carbon dioxide, produces oxygen and feeds the zooplankton, minnows and fingerlings above it in the food chain. The phytoplankton does best once the water is above about 60°F. Pond doses depend on volume and on what already lives in the water, so contact us and we will size it. For lakes and irrigation ponds, use Hydralife Compete instead.
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Storage
How long does Greenwater last, and how should I store it?
Use Greenwater when it arrives. If you plan to use it over a few days, give it gentle aeration for gas exchange and to keep the cells from settling, and refrigerate what you are not using yet. Give it a gentle shake before each use. Any extra Greenwater makes a great soil biostimulant for house plants.
Can I freeze Greenwater?
No. Freeze it and the cells do not survive, and Greenwater only works as live food. Refrigerate it instead, or keep it aerated under a strong light.
Source: FAO, 1996.
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Ordering and Shipping
AT A GLANCE
One 32 oz bag: $29.99. Two bags: $49.99. Three bags: $69.99. Five bags: $99.99, which works out to $20.00 a bag.
Subscribe biweekly or monthly and save 10 percent on every size.
Ships Monday through Thursday to the lower 48 states. Live arrival guaranteed.
What sizes does Greenwater come in, and what does it cost?
Greenwater comes in 32 oz breather bags: one bag is $29.99, two are $49.99, three are $69.99 and five are $99.99, which works out to $20.00 a bag. Subscriptions save 10 percent on every size. Commercial and bulk volumes are quoted per order.
Can I subscribe to regular Greenwater deliveries?
Yes. Biweekly and monthly subscriptions both save 10 percent, so a single bag is $26.99 per delivery. A subscription keeps fresh Greenwater arriving before a busy colony runs low, and you can cancel anytime.
When and where does Greenwater ship?
Greenwater ships Monday through Thursday by UPS or FedEx, delivered direct to the lower 48 states. Order by Sunday at 5 pm Mountain Time to receive it the same week, and tracking is emailed when the order goes to the carrier. Shipping Monday through Thursday means no order sits in a warehouse over a weekend.
Will Greenwater survive shipping in hot or cold weather?
Yes. Hydralife packages and ships Greenwater to arrive direct to you in any type of weather. It travels in insulated packaging and breather bags that let the culture exchange gas on the way, so the cells arrive active.
What if my Greenwater arrives dead or damaged?
Every order carries a live arrival guarantee: Hydralife replaces any bag that arrives dead or damaged. Contact us directly at 303.219.0623 or service@hydralifesolutions.com with any questions or complications with the product or the shipping carrier. Because Greenwater is a live product, it cannot be returned.
Do you sell larger or commercial volumes?
Yes. Commercial and bulk volumes of Greenwater are quoted per order. Call 303.219.0623 or email service@hydralifesolutions.com with your setup. For lake and irrigation-pond scale, ask about Hydralife Compete.
2 QUESTIONS
Greenwater vs. Hydralife Compete
What is the difference between Hydralife Greenwater and Hydralife Compete?
Hydralife Greenwater is a live feed for zooplankton cultures, fry and small ponds, while Hydralife Compete is concentrated phytoplankton for bioremediating lakes and irrigation ponds. Both use the same beneficial phytoplankton. Greenwater ships ready to pour in 32 oz breather bags. Compete is concentrated into buckets, dosed by surface acre and priced by the gallon, around $20 a gallon, to consume the nutrients that feed harmful algae.
Does Hydralife sell daphnia, moina or copepods?
No. Hydralife sells Greenwater, the live phytoplankton that feeds the daphnia, moina, copepods and rotifers you already keep. Pair Greenwater with a starter culture from a zooplankton supplier.
ASK US ABOUT YOUR CULTURE
Still have a question?
Every culture, fry tank and pond is different. Tell us what you are feeding, how many cultures you run and how often you feed, and we will size your Hydralife Greenwater order with you. Call 303.219.0623 or email service@hydralifesolutions.com.