What am I even growing?

"Algae" is not a scientific group. It is a loose word for plant-like things that live in water and photosynthesize. The word covers organisms as different from each other as you are from a mushroom. Some are bacteria. Some are protists. Some are close relatives of land plants.

What they share is the trick: they take light, water and carbon dioxide, and build themselves out of it. That is why growing them is so simple. You are not feeding them. You are giving them light and getting out of the way.

The algae we sell are microalgae, single cells you cannot see without a microscope, floating free in the water. A healthy culture looks like green paint. A very healthy culture looks like dark green paint. That colour is billions of cells per litre.

The five things algae need

• A container. Almost anything that holds water and lets light in.
• Water. Chlorine free. That is the one rule.
• Salts. The minerals dissolved in the water. To an alga, salts are what soil is to a land plant.
• Nutrients. Nitrogen, phosphorus, trace metals and vitamins. The fertilizer.
• Light. Twelve hours a day, on a timer, not too bright, not too hot.

That is it. There is no sixth thing.

• What are algae?
• Why algae matter
• Glossary of culture terms

Pick your strain

Start with what you want to do, not with what sounds interesting. Three strains cover almost every classroom and home project.

The three that beginners should choose from

• Spirulina (Arthrospira platensis). The forgiving one. It lives at pH 10, which is so alkaline that almost nothing else can compete with it, so your culture stays clean. Its trichomes are 20 to 1,000 micrometres, big enough to see and big enough to catch in a screen. It is the only strain we sell that you can harvest with a net. It is also the one people eat.
• Nannochloropsis sp. The fast one. A 2 micrometre marine cell that grows quickly, makes a lot of oxygen, and responds visibly to changes in light, salinity, nutrients and toxins. That responsiveness makes it the best strain for experiments. It will not settle out on its own, because the cell surface carries a negative charge and the cells repel each other.
• Chlorella vulgaris. The freshwater workhorse. Tough, fast, and it settles obligingly to the bottom when it is ripe, which makes it easy to concentrate without a centrifuge. This is the alga inside our algae beads.

Quick reference by strain

• Choosing a strain for your purpose
• Every strain we grow
• Nannochloropsis
• Chlorella
• Tetraselmis
• Thalassiosira
• Pyrocystis

What you actually need to buy

Less than you think. Here is the honest list, in the order it matters.

A container

Algae will grow in almost anything. What changes with size is how light gets in and how you mix it.

• Under 100 mL. A 50 mL centrifuge tube. Cheap, stands in a rack, good for running many treatments at once.
• Around 500 mL. A Beaker Bag or a recycled drinking water bottle with the lid resting on, not screwed down. This is the sweet spot for a classroom or a science fair.
• 1 to 10 litres. An Erlenmeyer flask or a tissue culture flask with a vented cap. Erlenmeyers swirl properly, which is why we use them.
• 10 gallons. A plain glass aquarium is the workhorse. Cheap, light gets in from every side.
• Bigger than that. Now light is your limit, not volume. The middle of a deep tank is dark. You need to mix, or go shallow and wide.

Light

An LED shop light and a timer. A single 36 watt LED shop light will run an entire classroom's worth of cultures. See section four for how close to put it.

Salts and nutrients

Buy the pre-measured salts for your strain and a vial of nutrients. You can mix your own from recipes, and we publish ours, but a bag of salts costs less than the chemicals and takes no time.

A Secchi Stick

Two dollars. It tells you how dense your culture is. It is the single most useful tool on this list and it costs less than a coffee. A spectrophotometer does the same job for three thousand dollars.

What we sell for each of these

You do not have to buy any of it from us. These are the versions we make and use ourselves.

Secchi Stick

Measures how dense your culture is. The one tool we would not go without.

From $2.00

View and add

Benchtop Algae Light

Built for cultures, not for houseplants. Put it on a 12 hour timer.

From $35.95

View and add

Beaker Bags

500 mL, graduated, stands up on its own, and a kid cannot break it.

From $2.95

View and add

f/2 Nutrient Media

The fertilizer. One millilitre per litre. One bottle grows 50 litres.

From $4.95

View and add

Seawater Salts

30 g/L, buffered. For every marine strain we sell.

From $3.95

View and add

Freshwater Salts

1 g/L. Yes, freshwater algae still needs salts. See section five.

From $2.95

View and add

Spirulina Alkali Salts

15 g/L. The pH 10 chemistry that keeps spirulina clean.

From $3.50

View and add

Complete Media Kit

Salts and nutrients together, pre-measured. The no-thinking option.

From $7.99

View and add

Things you probably do not need

• A heater. Only if your room drops below about 18 C at night. Most classrooms do not.
• An air pump. Below about a litre, shaking the bottle once a day does the same job. Above that, an air stone bubbling gently is worth it.
• A microscope. Lovely to have, not required. The colour of the culture tells you most of what you need.
• A CO2 system. No. Our salts carry a carbon buffer that supplies carbon for several batches.

• Culture vessels in detail
• Preparation
• Do I need a heater?

Light

This is where most cultures are lost, and almost never for the reason people expect. The problem is rarely too little light. It is heat.

What the numbers look like in real life

The flip side is worth knowing. A dense culture shades itself, so the cells near the middle are protected, and a large dense culture can take full sun happily as long as the water stays below about 32 C. A thin, young culture has no such protection. That is why we tell everyone to keep new cultures in dim light for the first two days.

What kind of light

• White LED. What we use. Efficient, long lived, very little waste heat, and the culture still looks green, which matters because green is how you judge health at a glance. Lighting from below looks great.
• Red and blue LED. Even more efficient, because they skip the green light algae mostly reflect. The downside is that your culture looks black and you lose your best health indicator.
• Fluorescent. Works well, little waste heat, but the tubes last about two years and contain mercury, so they must be recycled.
• Incandescent. No. Too much heat for the light you get.

• How much light do I need?
• Lighting for algae cultures
• Photosynthesis versus irradiance curves

Water, salts and nutrients

Water: the one rule

Chlorine free. Chlorine and chloramine are added to municipal water specifically to kill microorganisms, and your algae is a microorganism.

• Bottled water works, and spring water is the best of the bottled options. This is the easiest right answer.
• Well water is fine.
• Carbon filtered tap water removes chlorine.

Salts: the soil of the system

Salts are the physical and chemical environment. To an alga, dissolved salts are what soil is to a land plant. Our blends also carry a heavy carbon buffer, which slows pH swings and supplies carbon dioxide for photosynthesis, so our media holds denser cultures than plain seawater would.

A small amount of salt in freshwater media looks wrong, and is not. Those minerals supply trace elements and a carbon buffer that keeps pH stable. Distilled water alone grows almost nothing.

Nutrients: the fertilizer

Nutrients are what the cells build themselves out of: nitrate, phosphate, iron, a handful of trace metals, and vitamins. Our f/2 is a modified version of the Guillard and Ryther formula from 1962, adjusted so it works in fresh water as well as seawater.

• Dose: 1 mL of nutrients per litre of media. For a 5 gallon bucket, that is about 50 mL.
• You are very unlikely to overdose it. Toxicity does not start to appear until around 30 mL per litre, thirty times the normal dose. If you are worried you added too much, you almost certainly did not.
• After harvesting spirulina, replace 1 mL of nutrients for every 1 litre of culture you took out.

• f/2 media and its full composition
• Mix your own freshwater media
• Mix your own spirulina media
• What is in seawater
• Algae culture and pH
• How to measure salinity

Starting your culture

The day the box arrives

1. Open the box right away. Do not leave it on a hot porch or in a car.
2. Crack the bottle cap about a sixteenth of a turn. Not off, just loose. The culture needs to exchange gas with the air.
3. Put it somewhere you could comfortably read a book. Room light. Not a dark cupboard, not a sunny windowsill.
4. Start within 24 to 48 hours if you can. Opened and lit, a culture will hold for about a week, but sooner is better.

Making media

1. Dissolve the salts. Pour the bag into the right volume of chlorine free water and stir with a clean spoon until it is gone.
2. Deal with any precipitate. If it went white, stand it 24 hours, decant the clear water, discard the sludge.
3. Add the nutrients. One millilitre per litre. This is now called media. Store spare media somewhere cool and dark.

Inoculating

Inoculating just means adding your starter culture to the fresh media. There are two rules, and between them they prevent most failures we hear about.

1. Pour just enough media to cover the bottom of the vessel. You are not filling it. You are starting small and growing into the volume.
2. Add air and heat if you are using them. Bubble gently, just enough to make the media roll over. Hard bubbling shears cells.
3. Add the culture and mix.
4. Dim light for the first two days. The cells are adjusting. Bright light now is a stress, not a help.
5. Then move it into full light on a 12 hour timer, and shake or stir it at least once a day.

What happens next, and when

Every batch culture goes through the same four phases. Knowing them stops you worrying in week one and stops you being surprised in week four.

• Lag phase, day 1 to 10. Nothing visible happens. The culture is adapting. This is the phase people phone us about. It is normal. Wait.
• Exponential phase. The bloom. Growing as fast as conditions allow, and visibly greener by the day. Mix often.
• Stationary phase. Growth flattens because something has run out: light, carbon, or nutrients. The culture is at its densest.
• Decline. The crash. Resources are exhausted and biomass sinks. This is a normal end, not a failure. Refresh with new media and it comes back.

• Starting a project, in full
• Batch, semi-continuous and continuous culture
• Everything you can measure

Is it working? The Secchi Stick

"Is it growing?" is the most common question we get, and the answer is almost never a judgement call. Measure it.

A Secchi Stick is a black and white pattern on a ruler. You lower it into the culture until the pattern just disappears, and you read the depth. That depth is the Secchi Disk Depth, and it is a real measurement of optical density. Denser culture, shallower reading.

1. Lower the stick into the culture until you can only just make out the black and white pattern.
2. Read the depth in millimetres. That is your SDD.
3. Write it down with the date. One reading tells you nothing. A column of readings tells you everything.

We have measured our own strains against dry weight and cell count, so a Secchi reading converts to real biomass numbers. Those calibration charts are on the site for Nannochloropsis, Chlorella vulgaris and spirulina.

How dense is dense?

A healthy culture in a classroom is growing somewhere between 5 and 40 percent per day. A bottle that looks the same shade of green on Friday as it did on Monday is worth investigating. A bottle that is visibly darker is doing exactly what it should.

If you want the real numbers

• Secchi Stick, about $2. Optical density. Good enough for almost everything.
• Hemocytometer, $30 to $300. Counts actual cells under a microscope.
• Dry weight, free but fiddly. Filter a known volume, rinse the salts off, dry at 100 C for about half an hour, weigh it immediately. Rinsing matters. If you skip it you weigh the salt.
• Spectrophotometer, $3,500 and up. Absorbance at 750 nm. Precise, and mostly unnecessary.

Growth rate, if you need it for a report, is the specific growth rate: μ = ln(N2 / N1) / (t2 − t1), where N is your biomass measure and t is time.

• Measuring growth, in full
• Chlorella calibration chart
• Spirulina calibration chart
• Biomass lesson plan

When it goes wrong

Work down this list in order. The order matters, because it moves from most likely to least likely.

Nothing is happening

How long has it been? Lag phase runs 1 to 10 days. If it has been three days, wait. This is the single most common false alarm we get.

After that, check in this order:

1. Light. Is it actually bright on the culture, 12 hours a day, on a timer? Too dim is more common than too bright.
2. Temperature. Feel the bottle. Cold rooms slow everything down. Below about 18 C, growth crawls.
3. Water. Was it definitely chlorine free? Chloramine is the usual culprit and it is invisible.
4. Nutrients. Did they actually go in? One millilitre per litre. It is an easy step to skip.
5. Mixing. Shake it daily. Cells sitting still sit in their own exhausted water.

It went yellow, brown or pale

Colour loss means stress. Diagnose in this order:

1. Look at it under a microscope if you have one. Things swimming that should not be there means a grazer got in.
2. Light. Too much light bleaches pigment. Move it further from the lamp.
3. Temperature. Did it get hot? Over about 38 to 40 C most algae die, and pigment goes first.
4. Nutrients. An old culture that has used everything up goes pale. Add fresh media.

It went orange or bright yellow after a hot day

That is heat damage. Above roughly 104 F the pigment proteins denature. The culture is usually gone. Restart from your backup, and move it out of the sun.

Everything sank to the bottom

Sinking usually means the culture is starved, has finished its run, or both. Stressed cells produce sticky polysaccharides and clump together, and clumps sink. Try adding fresh media first. If it comes back, it was nutrients.

For Chlorella, settling at the end of a run is normal and is actually convenient, because it concentrates the harvest for you. For Nannochloropsis, settling is a warning sign, because a healthy Nannochloropsis culture will not settle.

Something is growing that I did not order

Contamination shows up as a colour that does not belong, a smell, a film on the glass, or specks you can see swimming. Options, in increasing order of effort:

• Filter the air going in. Four layers of paper towel taped over the air pump inlet stops a surprising amount.
• Dilute hard and keep the light up. A vigorous algae culture outcompetes a lot of things.
• Start over from your backup. Often faster than fighting it.
• Switch to spirulina if contamination keeps beating you. At pH 10 almost nothing else survives, which is exactly why we recommend it for difficult conditions.

Is my algae dead?

If it is green, it is alive. That is the short answer and it is right most of the time. Shake it, put it in good light, give it fresh media, and wait a week before giving up on it. Algae are far harder to kill than people expect.

• When is my culture dead?
• Stuff settling to the bottom
• Questions about algae beads

Harvesting

Getting algae out of water is harder than growing it. The cells are tiny, they are nearly the same density as the water, and there are a lot of them.

Screening, and why it only works for spirulina

The tightest mesh you can practically pour a culture through is about 30 micrometres. Anything finer clogs instantly. Spirulina trichomes are 20 to 1,000 micrometres, so they catch. Every other strain we sell is smaller than the mesh and goes straight through.

To harvest spirulina: pour the culture slowly through the harvesting screen. Keep the media that runs through and return it to the tank. Rinse the algae on the screen with cold tap water. When it starts behaving like a paste, it is done. Replace 1 mL of nutrients for every litre you took out.

Letting it settle

Free and slow. Chlorella settles willingly once it is ripe. Nannochloropsis will not, no matter how long you wait, because the cells carry a negative surface charge and repel each other.

Centrifuging

Fast, effective, expensive. A benchtop centrifuge handles small volumes. Flow-through and decanter centrifuges handle real volumes and cost real money.

Semi-continuous harvesting

The practical approach if you want a steady supply rather than one big harvest. When the culture reaches stationary phase, take half the volume, top it back up with fresh media, and the half you left behind is the inoculum for the next round. You never start over.

You know it is at stationary phase when the Secchi reading has been stable for two or three days and the colour is deep.

• Harvesting, in full
• Farming spirulina

Science fair projects that actually work

A good algae project has one thing you change, one thing you measure, and enough repeats that the result means something. Algae is nearly ideal for this, because you can run eight identical bottles on a windowsill and change one variable across them.

Projects that work

• Light intensity. Place bottles at measured distances from one lamp. Measure Secchi depth daily. Plot growth against distance. Simple, reliable, and it produces a real curve.
• Light colour. Same bottles, coloured filters. Green light should perform worst, because that is the colour algae reflect rather than absorb.
• Temperature. Several bottles held at different temperatures. Growth peaks then falls off a cliff. The cliff is the interesting part.
• Salinity tolerance. A series of bottles from fresh to full seawater. Different strains draw the line in different places.
• Toxicology, an LC50. A dilution series of some household substance, measuring at what concentration half the culture dies. This is a real technique used by real laboratories, and our Experiment Kit is built for it.
• Is my local water already fertilized? Culture water from a local pond or creek, half of it with added nutrients and half without. If both grow the same, that water already has all the nutrients it needs, which tells you something real about your neighbourhood.
• Grazing and predator-prey. Algae and brine shrimp together in a Beaker Bag. Count shrimp, measure algae, watch the two populations chase each other.

A worked example, start to finish

This is a complete project. If you follow it exactly you will have a real result, a real graph, and something honest to say at the table. Change the variable if you want a different question. The shape stays the same.

Projects that usually fail, and why we will tell you so

Some projects sound great and do not work in ten weeks on a kitchen counter. Lipid accumulation for biofuel is the usual one. It needs equipment you do not have, and even a professional lab with a half-time technician would have a good chance of getting nothing in that window. If you write to us with a plan, we will tell you honestly whether it will work, and suggest something that will. We would rather do that than sell you a kit for a project that disappoints you.

• How to form an experiment
• Science Fair Central
• Experiment and lesson plan ideas
• Bleach and algae blooms

Instructions for your kit

These are the short versions. Everything above explains why each step is there.