Culturing Phytoplankton

How to grow phytoplankton or green water!

Phytoplankton is a fundamental organism in the marine food web. It's growing in popularity as an additive for the reef aquarium and has long been a staple of aqua culturing facilities. Phytoplankton is a group of photosynthetic plankton composed of many species. Overall they are valuable as a source of nutrition for other tiny organisms with varying features depending on species.

Why grow Phytoplankton?

Some of the reasons to culture phytoplankton at home include raising rotifers for marine breeding, feeding other small crustaceans as a source of live food, and adding directly to a reef aquarium to increase the number of small beneficial organisms which may then feed your corals and fish. Phytoplankton is at the bottom of the food web and when used an additive it can help to improve the nutrition of all the animals above it.

Often when people are interested in breeding clownfish as well as other species of marine fish which require rotifers as a primary source of initial nutrition culturing phytoplankton can be the most economical solution to feeding the rotifers. While the larval fish do not eat phytoplankton, they do need a source of live food initially until they are large enough to be fed prepared foods such as crushed flakes or pellets. For clownfish this would mean rotifers, a tiny organism so small they are almost impossible to see with the naked eye. For the sheer number of rotifers that larval fish require, one must usually keep a live multiplying culture going, which is typically fed using phytoplankton.

How to grow phytoplankton

Growing phytoplankton at home can be very easy and usually inexpensive process. The process for growing phytoplankton in this article is designed for ease of use, access of materials and low cost. The materials suggested for culturing phytoplankton are as follows:

  • 2 Liter bottles (the quantity depends on how much phytoplankton you would like to grow, you should always use at least two)
  • Several feet of 1/4" air line tubing
  • Air pump (should be capable of running at least 2 air stones simultaneously)
  • Lighting (Fluorescent strip lighting works great)
  • Light Timer
  • Phytoplankton Starter culture
  • Phytoplankton food (Micro Algae Grow, Miracle Grow)

The first step should be to find a suitable place to setup your cultures. Often a closet or garage shelf can work well, the main concerns should be maintaining the culture at room temperature (temperature is not vital, but the culture shouldn't be allowed to get excessively cold or hot), and choosing a location where the lighting will not be an issue. Phytoplankton require light to undergo photosynthesis and reproduce. For this reason you must utilize some sort of strong but cool lighting for the phytoplankton cultures to grow an optimum rate. Fluorescent lighting is ideal because of its cool temperature and high output. A single CFL bulb could easily provide enough light for several bottles of phytoplankton. Incandescent bulbs should not be used unless placed at least a foot away to avoid heat transfer.

The setup is fairly simple once a location is chosen. After rinsing the 2 liter bottles out, you can drill a hole in the cap of the bottle to allow the air line tubing to reach the bottom, you want to allow the air to escape through this hole as well, so it should be somewhat larger than 1/4". The air line tubing connected to the pump should extend all the way down to the bottom of the bottle, the phytoplankton water should not be higher than 2-3" below the bottle's top. The bottles are then placed near a light source and will turn dark green within a week or two. The lighting should be turned on for about 16 hours a day with an 8 hour period of darkness.

Starting the culture from scratch

Unless you're reading this article as a refresher, this is likely your first time trying to grow phytoplankton. Once you have a culture going, every time you harvest you replace the saltwater and food source and the phytoplankton reproduce to replace those you harvested. This is a great cycle that prevents you from having too much other than add new saltwater and food. Before you can enjoy that cycle though, you need to get the initial phytoplankton culture going. Many online sources will sell phytoplankton cultures on an agar (nutritious gel medium) dish or in a bottle of suspended live plankton. The bottled version is the easiest method, but neither is difficult. If you order an agar dish you it will likely arrive with a set of instructions and what looks like a large Q-tip to remove the phytoplankton from the dish. You will be required to add a small amount of water to the agar dish to release the phytoplankton from the water. After waiting a short period of time you can use large Q-tip to gently rub the plankton off the agar and into the 2 liter bottles that were prepared with saltwater with a salinity of 25ppt. If you ordered the bottled version of phytoplankton than you can likely pour in the appropriate amount of phytoplankton as per the bottle's instructions. The amount of phytoplankton you initially start with is not important. Under the ideal conditions you would only need a single phytoplankton cell to start the culture, having more just speeds things up.

When you add first culture of phytoplankton to the bottles you need to also add the appropriate food for the phytoplankton to consume. When using a commercial phytoplankton food you can just follow the food's directions for 2 liters of water. When using Miracle Grow All Purpose Liquid Plant food, you should use approximately 5ml of the solution per 2 liter bottle.

Maintaining cultures

Maintaining a phytoplankton culture is easy and only requires a minimal amount of work but there are a few key things to do to prevent your culture from crashing and all of the phytoplankton dying.

  • Do not use air stones in the culture, they are unnecessary and difficult to clean, increasing chances of cross contamination.
  • Once a week, remove the air line tubing and cover the hole and shake the bottle to loosen any settled phytoplankton from the bottom of the bottle.
  • When harvesting phytoplankton, replace the amount harvested with an equal amount of 25ppt saltwater and the appropriate amount of food.
  • Do not cross contaminate your cultures with water from your aquarium and especially not from a rotifer culture if you have one.

Why keep multiple cultures at once?

It may seem like a good idea to consolidate your cultures into one single larger container but there are a few good reasons not to. The first and foremost is that by having multiple cultures you have a better chance of having viable phytoplankton to restart your cultures with. The more cultures you have going the better your odds of always having some available. In addition to the security provided with multiple cultures you also have a major convenience factor in using 2 liter bottles and being able to position them around your light source.

Dosing Phytoplankton in a Reef tank

Dosing phytoplankton in the reef tank can have various advantages depending on species of phytoplankton added. Whenever dosing a new product in your tank you should always take it very slowly and start at the minimum and gage its effect on your aquarium. It's often recommended that you dose between 1-3ml of phytoplankton per 10 gallons of tank water when using it as an additive. The amount will vary though depending on your culture's density and specifics of your aquarium. You can either drip the phytoplankton into the tank or pour it in at slow rate. It is very important to not over dose phytoplankton on a Reef aquarium. Phytoplankton is essentially liquid nutrients and excessive dosing could lead to rise in phosphates, nitrates and other pollutants. If you're experiencing excess algae problems, phytoplankton would be unlikely to help. The ideal tank to dose phytoplankton on would be a matured Reef tank that isn't experience excessive amount of nuisance algae.

Further reading:

Where to order phytoplankton cultures: