Culturing Phytoplankton For Reef Aquarium Food

Culturing Phytoplankton

Live microalgae is a natural food source used for feeding clams, sponges, soft coral, and other filter feeders.  It's rich in Omega-3 fatty acids, carbohydrates, lipids, and plant sterols.  As the foundation of the aquatic food chain, phytoplankton (phyto) provides food for zooplankton, which are then eaten by: stony coral, planktivores, and other invertebrates.  In addition, pods that feed on microalgae are more nutritious prey than pods which feed on detritus.

When we talk about phyto, we are usually referring to one or more of the thousands of species microalgae.  However, phytoplankton also includes other protists, including cyanobacteria and dinoflagellates.  For this article, phyto will mean microalgae (including diatoms, which are a type of brown microalgae that is often included in live phyto blends).

Live phyto blends, containing various species of microalgae, are available from local and online retailers.  Some of these products are filtered and concentrated.  However, the nutritional value of these cultures will still decrease when refrigerated, and cost (especially considering next day shipping) can become prohibitive.  In this article, I will discuss how to culture your own phytoplankton.

Nannochloropsis oculata

I am currently culturing the microalgae species, Nannochloropsis oculata.  It's often used to culture rotifers due to its high levels of vitamin B12 and Omega-3.  And while it's beneficial to copepods, larvae, and filter feeders, it has a relatively thick cell wall which makes it harder for certain animals to digest.[1]  Another species might be even more suitable if exclusively culturing phyto to raise copepods.

I started my culture using AlgaGen PhycoPure Greenwater (Nannochloropsis) which I purchased from Live Aquaria.  AlgaGen claims that customers have reported good results feeding Nannochloropsis to rotifers, copepods, amphipods, corals, shrimp, feather dusters, clams and other filter feeders.[2]  Plus, it's pretty easy to culture.

Florida Aqua Farms is another good source for a starter culture.  They also sell f/2 fertilizer, which has been used to culture microalgae for over 30 years.[3]  Live phyto blends purchased from your LFS can be used to start a culture; however, this will likely result in a monoculture of a single species (often Nannochloropsis).  Finally, a starter culture can come from another reefer who is culturing phyto (so check with your local reef club).

Phyto Culture Containers

Most commonly, hobbyists use one or more clear plastic two-liter bottles to culture microalgae, but you could use any size clear bottle with a cap.  I'm currently using two one-gallon Hawaiian Punch jugs.  Using two bottles helps ensure sustainability should one of the cultures crash.

Simply drill a hole in the cap for the airline tubing, leaving a little room for air to escape (to avoid the build up of air pressure, which could affect air flow).  I used a ¼” bit, which seems to work fine.  I have read where people have used filter floss to cover open gaps; but with a ¼" hole, this really isn't necessary.

I didn't bother to sterilize the bottles; I just rinsed them out.  However, I've read where others recommend sterilizing them prior to use.  Actually, I don't usually sterilized my containers or other equipment unless I'm doing a deep clean.  I do, however, try to keep everything rinsed clean and free of contamination from tank water.  Also, I make sure that none of the equipment which I use to culture rotifers is used for growing phyto.

Specific Gravity

Although most phyto species are pretty tolerant to various specific gravities, it's commonly recommended to culture phyto at 1.020 sg.  Likewise, rotifer cultures can tolerate a relatively wide range of salinities; however, they tend to be most productive between 1.014 and 1.017 sg.[1]  So if you are culturing rotifers, you might wish to culture your phyto using a lower specific gravity.  I'm currently culturing both my rotifers and phyto at 1.019 sg.

Always use new saltwater for your phyto cultures (never use water from your tank).  Contamination from tank water, or from a rotifer culture can compromise your phyto culture.  A ⅜ cup scoop of salt mix should make a gallon of saltwater with a suitable specific gravity.  I'm using a scoop that was included with some protein powder.  These scoops come in various sizes, so test it first (mine mixes one gallon of RO/DI water to 1.019 sg).  But just like in a reef tank, a specific salinity isn't as critical as consistency.

Dosing Nutrients and Trace Elements

Nitrate and phosphate are needed to grow microalgae; but trace elements (like iron, copper, zinc and manganese) are needed too.  In addition, brown/tan microalgae (diatoms) need silicate.  In order to supply our cultures with these elements and nutrients, we dose fertilizers with trace elements.

When starting a new culture or splitting an existing culture, add 1.5 ml of Guillard f/2 fertilizer for each two-liter bottle.  I recommend using Micro Algae Grow from Florida Aqua Farms.  However, it's possible to use Miracle-Gro Liquid All Purpose Plant Food by adding Kent Essential Elements.  But I'm not exactly sure of the correct dosages, and Miracle-Gro might contain ingredients and/or quantities that are not ideal for reef tanks.

Dosage notes: 20 drops is roughly equal to 1ml.

• Use 3 ml (60 drops) of f/2 per each gallon, when starting or splitting a culture.
• Use 1.5 ml (30 drops) of f/2 per each two-liter bottle, when starting or splitting a culture.
• Use ¾ ml (15 drops) of f/2 per each liter, when starting or splitting a culture.
• Use ⅓ ml (7 drops) of f/2 per each pint, when starting or splitting a culture.

Aeration

Aeration is necessary to supply carbon dioxide for photosynthesis and to help maintain pH.  However, excessive aeration can potentially fracture the cells and cause foaming.[1]  Air stones aren't necessary, but I have used them with Nannochloropsis in the past without problems.  Instead of air stones, most people recommend using rigid air line tubing.  In addition, you'll need an air pump, flexible air line tubing, a gang valve, and a check valve.

Aeration also circulates the non-motile algae, which exposes the individual cells to the light and helps prevent them from settling to the bottom.  You can occasionally (like once or twice a week) gently shake the culture(s), but this generally isn't necessary.  I have an extra cap (without a hole in it) in order to shake my bottles without spilling the culture; but you could just put your finger over the hole in the cap instead.

Temperature

Room temperature is typically fine.  Plus, you don't want to use incandescent light bulbs for lighting, as they may heat the culture too much.

Lighting

I originally used compact florescent work lights, but I had one melt down and nearly caused a fire; so I switched to a plastic clamp-on light with a standard 75W equivalent LED light bulb (daylight spectrum).  I leave the light on 24/7, but 16 hours a day would be adequate.  Try to light the side of the bottle(s), versus just the top (which is smaller and partially blocked by the cap).

Harvesting Phyto Weekly

I keep the culture going by harvesting it weekly as follows:

• Make enough new (1.019 sg) saltwater to dilute your culture in half (one gallon in my case); then let the salt mix dissolve thoroughly.
• Pour half of the culture to be harvested into a bucket with the fully dissolved saltwater (this will be your new diluted culture).  The other half can be used to dose your reef tank(s), maintain a pod culture, or stored for future use.  You can optionally remove larger particles from the culture by pre-straining it through a 53 micron plankton sieve (available through Amazon).  Nannochloropsis is only about 4 to 6 microns in diameter.[1]
• Clean the culture bottle(s) with a bottle brush.  If needed, you can use vinegar to help clean it.  A bleach solution could also be used to clean and sanitize the bottle (just make sure that you thoroughly rinse and dechlorinate it afterwards).
• With the help of a funnel, pour the newly diluted culture back into the clean culture bottle(s).
• Add 1.5 ml of f/2 fertilizer into each two-liter bottle (or in my case, 3 ml into each one-gallon bottle).

Notes:

• Harvest your cultures once a week.
• Foaming on top of the culture can indicate that harvesting is overdue.
• If using more than one culture bottle, you could potentially harvest them on different days.
• When starting a new culture, it might look fairly pale in color.  If so, let it darken up before you start harvesting it.  However, you should continue to add f/2 weekly (and give the culture a gentle shake).  You'd be surprised just how small of a phyto sample is required to start a new culture.

Storage

Freshly harvested phyto provides the best nutrition.  However, it's possible to store it when necessary.  Use (clean) empty water bottles to store harvested phyto in a refrigerator.  Label them with a date so that you know how old they are, and so that nobody mistakes it for something else.  You can keep phyto in the refrigerator for up to a month (keeping in mind that its quality will continue to degrade with time).

Dosing Phytoplankton

Gently shake or invert the refrigerated phyto bottle at least once a week, and before dosing.  You can either broadcast feed your tank, or target feed specific specimens with the help of a clean syringe, pipette, or eye dropper.  I suggest target feeding any livestock that requires phytoplankton.  This can be done by releasing the phyto a couple of inches upstream from the target.  When using a pipette (or another tool) to feed, avoid contamination of your phyto by pouring it into another container first.

To broadcast feed your tank, start slowly.  Dose it into a high flow area of your tank.  Eventually you can increase the dosage and/or frequency.  It has been said that excessive dosing could negatively affect water quality, but I haven't found that to be the case.  Still, it's a good idea to monitor your tank's nutrient levels when you first start dosing, or if you change how much you're dosing.  I might start dosing a few milliliters per gallon each week and adjust from there.  It's not unusual for me to dump an entire liter of phyto into my 40 gallon tank (which is enough to tint the water green).

Water Quality

I tested my phyto culture for phosphorus just prior to harvesting it by diluting a sample with 9 parts of clean saltwater. Through that, I determined that the undiluted phosphorus concentration was 310 ppb (or roughly 0.95 ppm of phosphate), which was actually lower than I had expected.

There are about 3,785 ml in a gallon, so dosing 1 ml per gallon would cause an immediate increase in phosphorus of just about 0.08 ppb (or about a 0.00025 ppm increase in phosphate).  That's really not that much phosphate.

Nutrient Consumption

AlgaGen states that Nannochloropsis, “is also known to be a great water conditioner” consuming and binding nitrate, phosphate, and heavy metals.[4]  This is contrary to phyto's reputation for adding phosphate to your tank (which, as I indicated above, it initially does).  However, I assume that the live phyto continues to consume nutrients within our reef tanks after dosing, potentially lowering nutrient levels (versus raising them).

Resources:

1. Wilkerson, Joyce D.. Clownfishes. Microcosm Ltd.. Kindle Edition.
2. https://www.liveaquaria.com/product/3249/phycopure-green-water
3. http://floridaaquafarms.com/
4. https://www.algagen.com/phycopure1.html