The AK Culturi-M is the bigger reactor in the Culturi range, running 2 L of phytoplankton, macro-algae, or microfauna in a sealed glass vessel with integrated lighting and gate-valve airflow. Built for growers who want steady output without the DIY fuss, whether that is feeding multiple systems or scaling a single culture.
For box contents, specifications, and compatible add-ons (including the optional Pod Core for copepod cultures), see the product page.
The glass vessel is not fixed to the base unit, it is held in only by friction. Please ensure you show extreme care similar to how you would treat any glass equipment.
This unit contains multiple glass components. Handle all glass parts with extreme care, including the rigid glass tubing and the glass vessel, to avoid injury or damage.
When inserting the rigid tubing into the seal, lubricant is usually not required. In most cases, the tubing should slide into place with only very light pressure, about the weight of one or two fingers. Insert it slowly and stop when the end of the tubing is approximately one finger width above the bottom of the vessel. Forcing it too far or too quickly may fracture the base of the vessel and may also damage the light unit.
If additional slip is needed, use a food safe lubricant such as USP or food grade glycerin, or a small amount of sterile water based lubricant. Cooking oil should only be used as a last resort.
Because the vessel may be filled with water during use, any fracture could also result in water damage to the light unit and surrounding area if proper care is not taken.
After installation, thoroughly wipe the tubing clean on both the inside and outside of the vessel to remove any lubricant residue before use.
WARNING: It is highly advised that the rigid tubing is removed before removing the lid from the vessel. This is especially important if you are using the Pod Core as you may risk damaging the tubing or vessel and potentially injuring yourself if any glass were to break.
Good, clean cultures are not possible without good, clean sterilisation. Massively reduce risks of cultures crashing by sterilising at every opportunity.
There are a few different options for sterilisation ranging from simple and safe, to extremely effective but potentially dangerous to your skin and eyes.
We'll stick with the simple and safe ones here, but if you're confident we do recommend researching tougher methods.
White Vinegar
Diluted Isopropyl Alcohol
Isopropyl alcohol makes for effective sterilisation, If you have 100% isopropyl alcohol it is recommended to dilute it with water to 70% to prevent it evaporating before it can even become effective.
Avoid adding boiling water to the vessel, or rapidly changing the vessel's temperature as it may fracture the glass.
We highly recommend synthetic salt as you will not have to sterilise the water. If you only have natural seawater as an option we highly recommend sterilising it also so that any microorganisms it hosts don't consume what you're trying to grow.
If you intend to use natural seawater, we recommend neutralising life inside it with chlorine, and then neutralising the chlorine with thiosulphate, you've done it right if you can smell chlorine before, but not after adding thiosulphate.
You should attempt to match the salinity of the starter culture you have, you could consult your supplier for the exact specific gravity, or in most circumstances, 1.022-1.026sg (30-35ppt) suits most strains. Some strains prefer the lower end of that range, others the higher end. The Lighting & Salinity section lists the values we recommend per strain.
These are the brightness and salinity settings we recommend per strain.
Please refer to the "Preparing Saltwater" section above before continuing...
Once you have your saltwater prepared, fill the glass vessel up with 1.8 litres of clean fresh saltwater. You will need the remaining volume for adding your starter culture.
For fertiliser, you will want to use Guillard's F/2 for most strains (e.g. nannochloropsis, tetraselmis). Follow the instructions carefully adding the required amount to your glass vessel, do not stir with anything that hasn't been appropriately sterilised.
It's a good idea to ensure the fertiliser is well distributed within the water before continuing on with the next step, simply stir the water or swirl the vessel carefully - though not doing this may not be detrimental to the success of your culture we do recommend it to prevent any concentrated amounts of fertiliser damaging sensitive cell walls.
To give an exact amount of how much phytoplankton you need to begin a culture, would be: 1 single cell.
That's correct, that's all it takes, we do highly recommend adding more though with a 9:1 water-to-starter-culture ratio being the safe margin.For the Culturi-M that means 1.8 L saltwater with 200 mL starter culture (which is a generous start, you'd likely still succeed with 50 mL)
Turn on the unit's integrated light if you haven't already and add your desired starting amount.
Phytoplankton generally performs best under strong aeration. Turn on the air pump, then open the gate valve attached to the rigid tubing fully, or as far as it will allow, to provide a high level of airflow. This helps keep the culture well mixed, improves gas exchange, and prevents cells from settling at the bottom. For most common phytoplankton strains, this level of airflow is suitable and supports consistent growth.
If everything was done correctly, your phytoplankton will begin to darken, often slowly for the first day or two, then quite noticeably day after day from there.
Keep the water between 18-25°C (64-77°F). Above 26°C the culture will stress, so if it is climbing too high, lower the brightness to reduce the heat from the light.
If you find that it is growing too quickly, lower the amount of time it receives light, and do the opposite if it's growing too slowly.
You may experiment with adding more fertiliser to achieve your desired density.
Depending on your light schedule and brightness, you may reach the harvest point earlier than shown below, in that case, you should harvest as soon as possible.
Highest density and maximum health is typically found around the 5th and 7th day. Simply pour the contents of the vessel into a clean 2 L bottle and store it in the fridge unless you intend to use it immediately. (refrigeration prolongs life significantly). Keep the amount of time the phytoplankton is exposed to air at a minimum. Avoid collecting dead or dying cells that rest at the bottom of the culture, healthy phytoplankton will be in the water column.
After every harvest you should reset the culture back to the beginning by sterilising everything. It may seem unnecessary but it is paramount to eradicate any airborne bacteria that may have made it's way in before it begins to thrive on your sequential cultures.
Based on our experience, neglecting to properly reset is starting the clock on your culture's downfall.
After properly cleaning everything, repeat the process from Step 1: Filling up.
To culture copepods successfully, you will need a reliable and ongoing supply of phytoplankton. Many users choose to run a second AK Culturi-M or AK Culturi-S specifically for phytoplankton production so they can comfortably keep up with the daily consumption of their copepod culture.
Typical phytoplankton consumption for an AK Culturi-M copepod culture is around 10 to 50 mL per day, depending on culture density. Consumption may be even higher if rotifers are present, which is common, as they are often included with copepod cultures at some stage of their lifecycle. This is perfectly normal, and they can coexist without issue.
Copepod cultures usually go through an initial settling-in period as they adjust to their new environment. This is essentially environmental shock, and it can take 2 to 3 weeks before the culture begins to establish properly. With this in mind, do not be discouraged if you are not seeing large numbers during the first few weeks. In many cases, meaningful population growth is not observed until around week 4.
During this initial period, the main thing to look for is ongoing life within the vessel. As long as you can still spot the occasional copepod moving through the culture, the culture is still active. Seeing a female carrying eggs in her brood sack is an especially reassuring sign.
Always source copepods from a reputable vendor. Ideally, the culture should be started using the water the copepods arrive in, as this helps reduce environmental change and may shorten the initial settling-in period. Avoid introducing bottles that contain detritus worms, flatworms, hydroids, or anything else that is clearly not a copepod. Some visible detritus is perfectly normal and is often just clumped phytoplankton cells. If you are unsure whether a bottle is clean, we are happy to help identify what you are seeing.
Copepods are generally hardy and can tolerate a fairly wide range of temperatures and salinities. In most cases, acclimation is not necessary.
If you have purchased our Pod Core, gently place it into the glass vessel before proceeding to the next step.
If you are using the Pod Core ensure that the rigid tubing is fully retracted or removed before removing the lid, as the risk of snapping the rigid tubing is much greater with this optional attachment inserted.
Before continuing, please refer to the Preparing Saltwater section at the beginning of this guide.
Start by adding 100 mL of freshly prepared saltwater to the vessel.
From here, there are two acceptable approaches depending on how confident you are in the source culture.
If the copepods were purchased from a reputable and trusted vendor, and the bottle appears free from any other unrecognisable organisms, the entire contents of the bottle may be poured directly into the glass vessel.
If you would prefer to take a more cautious approach, use a pipette to extract as many copepods as possible from the bottle while transferring as little of the original water as possible. Dispense them directly into the vessel.
The exact amount of water introduced at this stage is not especially important. From this point onward, simply add 100 mL of fresh saltwater per day until the culture reaches the max fill line. This gradual increase helps expand the culture volume and available surface area over time while minimising environmental stress.
Keep in mind that each feeding will also contribute to the total water volume. If the vessel reaches the max fill line before the culture has established strongly, some water will need to be removed so feeding can continue as outlined in the next section.
The most effective food source for copepods sits right at the base of the food chain: phytoplankton.
In most cases, Nannochloropsis is more than sufficient to support strong culture performance and high harvest yields. While there can be value in feeding a blend of phytoplankton strains, care should be taken when doing so. Some strains have a shorter lifespan than Nannochloropsis and may foul the water more quickly if they are not consumed in time.
Feeding is straightforward, but the amount required will vary depending on both phytoplankton density and the current water volume of the culture.
As a general guide, the water should maintain a light green tint after feeding. A good visual reference is to imagine adding a single drop of green food colouring to a 2 litre body of water. The culture water should appear lightly tinted, not dark or heavily saturated.
The goal is to provide enough phytoplankton to keep food available within the culture without overloading the vessel or allowing excess algae to accumulate and degrade water quality.
Phytoplankton can be concentrated before feeding by allowing it to settle in a bottle until the cells separate from the surrounding water. Once settled, gently pour off the clearer water from the top until only a small amount remains. Then swirl the bottle to resuspend the settled cells into a dense, concentrated feed.
This is especially useful when feeding copepods, as it allows you to add more nutrition without significantly increasing the overall water volume of the culture.
Turn on the air pump, then promptly adjust the airflow using the gate valve connected to the top of the rigid tubing. Reduce the airflow until the culture is receiving no more than 2 to 3 bubbles per second.
The goal is to maintain gentle aeration without creating unnecessary turbulence within the vessel.
As mentioned earlier, copepod cultures may appear to progress slowly during the first 2 to 3 weeks. During this initial establishment period, harvesting should be avoided until the population has clearly begun to expand.
Throughout this time, you may notice detritus gradually building up within the vessel. This is completely normal. We strongly recommend leaving it undisturbed, as attempts to remove it have consistently been shown to disrupt the balance of the culture and can lead to collapse.
Most copepod species prefer very low light levels due to their natural survival instincts. In the wild, light often means exposure, and exposure can mean predators. While lighting can still play a useful role in copepod culture, it should be approached carefully.
White light can encourage algae growth, and algae can serve as a food source for copepods. However, excessive light intensity may place unnecessary stress on the culture. Put simply, while some light can be beneficial, too much can work against the conditions copepods naturally prefer.
For this reason, we recommend running the light on a schedule from 6:00am to 5:00pm at 5% brightness. This provides enough light to support visibility and mild algae growth without heavily disturbing the culture.
If you need to check culture density, the brightness may be temporarily increased to 100% for inspection. Once complete, return the light to its normal setting.
If you are using a Pod Core, a slightly higher light level may be beneficial. This can help encourage copepods to move deeper into the core structure, making better use of the available surface area and shelter. Any increase should still be kept modest to avoid unnecessarily stressing the culture.
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