10 How to Maintain
This is the last part of the 'How-To'. There will be a series of videos for each tip, so stay tuned!
10.1.1 Light
• If your culture is yellowish or green-olive it means that the Spirulina cells are under too much light and the cells are lysing. You need to shade the culture now!
• When Spirulina is good and strong the rule of thumb with light is the more the better. Sunlight is best and will provide the most growth for your Spirulina. The more surface area of your growing medium that is exposed to sunlight, the better—for only when Spirulina is established and strong. However, when you are first growing your Spirulina, too much sunshine can hurt them. Shade the container by placing a sheer fabric over your tank. See-through white fabric is best, but if you don't have that experiment with what you do have. The rule of thumb is that if you can see through your medium then it is a good idea to shade it. Once the green spirulina has grown thick enough that you can't see through the tank then take off the fabric.
• If you don’t want to wrap your vessel in fabric, you can simply shade it with a curtain and use the LED as the sole light source.
10.1.2 Artificial Light
• Ordinary 'grow lights' which are optimised for green land plants, are not particularly good for growing Spirulina or other blue-green algae (though they will work). A light with more red and orange light—i.e. a 'warmer' colour—would be more efficient for growth.
• Pick a light that has a warmer colour (625 – 650 nm). It allows Spirulina to absorb a higher fraction of the light and increase the growth rate. Put the lights on a timer and set the timer on 16 hours of light per day. Spirulina does need a rotation of day and night to strive.
• I've been using an LED corn bulb 2700K-3000K (warm white) 1500 lumens—it's been great!
10.2 Agitation
• When the tank has efficient circulation, all the Spirulina cells are mixed in the water column and get plenty of sunlight, each in turn. No agitation in the tank means that Spirulina cells won’t get as much sun and won’t produce as much as they could. A proper agitation is also very important to prevent Spirulina from forming clumps on the surface of your container!
Stirring your tank will force spirulina filaments to go up and down in the water column, to go to the surface and then descend, limiting the time each filament will be exposed to the sunlight. Ideally, you want each Spirulina filament to stay about half a minute at the surface.
• Aeration rate is a key parameter to improve the growth of the microalgae cell. This reduces nutrients gradient, avoids cell sedimentation, clumping, fouling, and dead zones; it can create an optimised light/dark cycle that can enhance the photosynthesis. However, excessive aeration may produce cell damage.
• As you learned in 7.8 and 7.9, you must adjust the pressure over time to find/maintain the right balance.
10.3 Temperature
• The optimum temperature for maximal growth is 35 – 37℃ (95º- 98℉).
•  Don't go over 39℃/102℉ (it will die) and below 15.5℃/60℉ (it won't grow well).
• Though many sources recommend using a heater; I don't think it is necessary. I’ve tried both ways and discovered if it gets enough sunlight during the day and artificial light during the night, it is fine. If you live in a very cold place that doesn't have a heating system, when the weather is cold it might sink to the bottom or stick together—that's totally normal and fine.
My room temperature during the winter is around 22-25℃ and it's been fine. I once placed another container in my college (no heating system), I didn't check but I estimated it was 19-20℃, it didn't grow quickly at first, but once it adapted to the climate it grew quite well.
• If you have a lot of sunlight you need to be aware of how much heat is added to your tank during the sunniest times of the day. You may be surprised at how the temperature will rise. Be sure to monitor this as you are learning to grow your Spirulina and as the seasons change.

Healthy colour!

Left: alive and healthy | Right: absolutely dead

10.4 Colour/Smell
•  Colour of the culture
→ Yellow-green/lime green = too much light
→ Blue-green = healthy
→ Yellow = dead
→ White = dead
•  Colour of the growing medium
→ Clear = new
→ Yellowish = old (needs to renew)
• Always pay attention to the colour and smell of your Spirulina. Do not eat anything that is clear, white, yellowish or stinky. Spirulina should be very dark green and have a neutral seaweed smell and taste.
10.5 pH
• When starting out, the pH should be around 8.5 and it will slowly rise as the days go by.
• Never eat your spirulina if the pH is below 10 or above 11. If pH is below 10 but looks thick give it a couple of days and the pH should rise and you can harvest. If this doesn’t happen consider adding more nutrients. If your pH has risen to 11 or above it is time to change your growing medium.
[source: How to Grow Spirulina at Home​​​​​​]
10.6 Clumps Cleaning + Reducing Tips​​​​​​​
• It is normal for the algae to coagulate in clumps as they grow. This is one of the reasons for keeping the medium moving along the edges of the tank, to inhibit clump growth. You will find that as you maintain and harvest your algae that clumps will detach and float at the top of the water. It is okay to filter and consume clumps that are very dark blue-green. Do not eat any clumps which are clear, white or yellowish. These clumps are a normal part of the spirulina process. Just remove them from the medium using a small strainer or spoon and dispose of them.
[source: How to Grow Spirulina at Home]​​​​​​​
• Regarding the source above, I find it much easier and quicker to clean the clumps by using a spatula (same one as I use for the harvest). Simply sweep the clumps to the edges of the glass surface, then wipe them off. I tried using a strainer but the healthy culture got sucked in as well, so I've avoided it.
• Having an air pump connected to a plugin timer can help reduce clumps. Before I owned a timer, I switched on the air pump after I woke up and switched it off before going to bed - I thought there's no need for agitation when there's no light. When there's no agitation for a long period, Spirulina can either float or sink depending on conditions. I've found that intermittent agitation during the night has decreased the amount of clumps significantly. I've got the timer set to agitate every hour for 15 minutes while I sleep.

Freshly diluted Spirulina

Fully grown Spirulina

10.7 Backup Culture
• Keep a bottle of safety culture separated from your tank. This can be any glass bottle or jar that has a fabric cover to let air in but no contaminants. This safety bottle does not need to be aerated or heated. Keep it in the sunlight. It will grow slowly, but that is fine. Swirl this bottle as often as you remember, once a day is best. Change it out if you notice any discolouration or about every couple of weeks or month. It is good to keep one or two of these as a backup plan in case anything happens to your main tank.
[source: How to Grow Spirulina at Home]​​​​​​​
• Regarding the source above, I've tried both options: swirling manually and aerated by connecting to the air pump. I've found that aeration decreased clumps just like I stated above (10.6) but in this case, the difference wasn't that significant. However, I'd encourage you to aerate it anyway since you'd already have an air pump that can be connected to multiple containers—take advantage of its ability and use it more efficiently.
10.8 Going on Vacation
• The trick is to slow down its metabolism by lowering the tank temperature. This can be done simply by turning off the heater. The tank should also be kept from strong direct light during this time as well, although it does need some light. If kept in this way, it should be fine for several weeks or more. When bringing it back from this state, raise the temperature and light in stages, over a few days, and the algae will be fine.
10.9 Renew the Culture Medium Every 4-6 Months
• If the proper amount of make-up mix (nutrients) is added back to the tank after every harvest, the nutrient balance can be maintained for a high level of growth for about four to six months, at which point the pH will have risen too high (11+) for good growth. At this point, you simply mix up a new batch of medium, harvest all your Spirulina, and immediately put them in the new medium. After a couple of weeks, your culture should be full, dense, and ready for harvest again, ready to start the 4-6 month cycle. So, you need enough starter mix to renew your culture every 4-6 months.
[source: Algae Industry Magazine]​​​​​​​
• You will do this when your pH reaches 11, or if you suspect that your chemistry is off because your colour is yellowish or Spirulina isn’t growing well. The idea here is to strain out all of your culture and put it in fresh clean medium. Strain out your entire culture from your tank. Do it just like you do when you harvest, though you do not need to squeeze Spirulina completely dry. Each time you strain a bucket of the old medium, empty the strained spirulina from your fabric into the new bucket with fresh growing medium.
10.10 Morphology Observation
• Interestingly, Spirulina has a built-in mechanism to protect itself against too much sunlight.
Most Spirulina strains can exist under two forms – in spiral and straight. Each species of Spirulina has its own specific spiral form. The same species can also have different forms in the function of the environment (area in the world) where it is found. When Spirulina cells don’t have enough light they will straighten themselves so that they can absorb more light. When the sun is too intense, they will become more spirally, each turn of spiral providing some shade to the rest of the filament. Even if straight spirulina has the same nutritional value as the spiral form, it is more difficult to harvest. So in general, this is something you want to avoid.
Message from the Creator
Congratulations, you've just learnt all the principles. Growing Spirulina at home is not an easy task, but with the right kind of knowledge and tools, you will make it look easy!
Want to Learn More?
There are several sources (online/offline) that I've learnt from. I urge you to read/research continually as this is very important in being able to identify and overcome some challenges with ease. If you have time please come back later and look through them.
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