Living in San Jose means your apartments aren’t always big. After setting up my reef in just four square feet of living space, I learned to appreciate every piece of equipment that serves multiple purposes. Filtration that also contributes nutrients to your system isn’t nice to have when your 40-litre nano reef has zero room for a sump, it’s required. Chaetomorpha, or chaeto, is one of those things.
Chaeto is most commonly known as refugium algae, but few people realise how efficient of a biological filter it actually is. Chaeto filters nitrates and phosphates directly from your water column (Live Algae UK), houses copepods and microfauna, and can stabilise your pH through photosynthesis. In nano setups where every light and bottle must justify its footprint and running costs, chaeto provides tangible water quality benefits without using anything more than light.
Chaeto grows faster and occupies less space than your typical bulb or strand-style macroalgae species. Unlike Caulerpa, chaeto doesn’t crash overnight if your parameters dip. It’s less picky about lighting and water conditions than red macroalgae. Chaeto just grows. Week after week, it pulls nutrients out of your water and can be harvested.
## How Chaeto Filters Your Tank
Photosynthetic Nutrient Export: Chaetomorpha excel at removing nitrogen and phosphorus from your tank through photosynthesis. While bacterial filtration will convert toxic ammonia to less harmful nitrate, chaeto literally eats the nitrate out of your water column. Harvested chaeto is then physically removed from your system, permanently exporting those nutrients.
Studies into aquaculture have demonstrated macroalgae’s capabilities in nutrient removal from closed systems. Aquaculture farms actively use macroalgae filtration because of its reliability and ease of use.
Because chaeto pulls nutrients out of the water column, it will compete with nuisance algae growing inside your aquarium. Dense purple/pink slime algae on rocks? Chaeto may help. Hair algae in every corner of your live rock? Chaeto eats nutrients the hair algae needs to survive.
pH Stability: Similar to Caribbean hitchhikers Ricordia coral, chaeto consumes CO2 during the day which increases your pH. It’s subtle but very noticeable in my smaller tank. By running your chaeto lighting at a reverse photoperiod from your main tank, you’ll get 24-hour pH stability as your chaeto is producing oxygen and consuming CO2 while your main tank is dark and respiring.
This process even increases gas exchange efficiency in your tank. As chaeto photosynthesises during it’s light period, it is using up CO2 and producing oxygen. Many reef keepers even notice improved colouration and willingness to eat from their corals when adding chaeto to their systems.
Refugium Habitat: On top of nutrient export and pH stabilisation, chaeto provides an excellent habitat for copepods, amphipods, and other microfauna to flourish and reproduce. These creatures help to feed your fish while processing detritus and matter throughout your aquarium. Basically, chaeto gives you double the biological filtration.
## Primary Use: Refugium
Refugium Lighting: Chaeto needs 12-16 hours of quality lighting to perform all of these jobs (Bulk Reef Supply). Most successful reef keepers aim for a PAR value of 100-200 which can be accomplished with cheap refugium LED lights or even regular plant grow lights (Reef2Reef).
I couldn’t get decent growth on my chaeto using my regular aquarium LED on a timer. Once I switched to a refugium light with true red and blue spectrum LEDs, growth took off within 3 weeks. What was once a barely there clump of algae doubled in size in a month.
If you’re tight on budget or have a small nano tank, try using one of those clip on plant growing LEDs you can find at Walmart. Look for something that puts out at least 30 watts over the area of your refugium and includes true red and blue diodes. No cheap pure white LEDs or blue-only LEDs as those won’t allow your chaeto to grow properly.
Reverse Lighting Photoperiod: To get the most benefit from your chaeto’s pH stabilisation abilities, run your refugium light opposite of your main tank lighting (Reef2Reef). When your tank lights turn off for the night and your tank begins to respire CO2, your chaeto turns on and begins consuming CO2 through photosynthesis. Not only does this provide a more stable pH throughout the day, but better water parameters overall.
Try setting your chaeto light timer to turn on 30 minutes before your main tank lights turn off, and turn off 30 minutes after your main lights turn on. This way you never have a gap in photosynthetic activity from either light source and will provide maximum pH support. If your aquarium controller allows, set it up this way. Otherwise, two separate timers are easy enough if you’re running basic equipment.
Flow & Placement: Chaeto doesn’t require a ton of flow, but be sure there is enough movement to reach the entire surface area of the algae. It also helps prevent detritus from building up in the centre of your chaeto where dead spots are likely to occur. Think enough flow to sway your chaeto back and forth, but not so strong that it tears apart.
Ideally, in sump refugiums place your chaeto in the middle chamber. Flow should be moderate at this point, pushing through your mechanical filtration but before it reaches your return pump. If you have a hang on back refugium, or something like a Chaetogonium reactor, position it near the output of a small powerhead on it’s lowest setting or where overflow from your tank will create natural flow.
Water Parameters: Like most macroalgae, chaeto prefers standard reef water parameters. Aim for around 35 ppt salinity or 1.026 specific gravity (Aquifarm). Temperature should be similar to what you keep your reef at, around 22-26°C. Chaeto can handle slight fluctuations in parameters better than many starter algae species. This makes it a great choice for beginners still getting used to water changes and maintaining consistency.
Try and keep your alkalinity between 8-12 dKH and calcium at appropriate levels for your coral needs. Chaeto doesn’t consume much calcium from your water, but keeping parameters stable will acclimate the algae to your system and prevent sudden swings that could kill it.
| Refugium Volume | Chaeto Amount | Lighting Requirements | Approximate Monthly Costs |
| ————— | ————- | ——————— | ————————- |
| 10-20 Litres HOB Refugium | Tennis ball size chunk | 15-25 Watts clip on | £8-12 for electricity |
| 40 Litre Sump Section | Softball size chunk | 30-40 Watt dedicated refugium LED | £12-18 for electricity |
| 80+ Litres Dedicated Refugium | Several handfuls | 50+ Watts full spectrum light | £15-25 for electricity |
| One time costs will vary. | Usually £15-30 for live chaeto starter culture | £25-150 depending on fixtures chosen. | harvesting time every few weeks. |
## Common Mistakes People Make
Not enough light! I see this so often in aquarium forums. People try to use a basic aquarium LED or run their chaeto under the spillover from their main display. Chaeto requires dedicated lighting for 12-16 hours per day to stay healthy and process nutrients. Weak aquarium LEDs or not enough light time will result in lazy growth and even death.
Adding too much chaeto at once. This algae needs time to adjust to your specific water conditions. Even if you have perfect parameters, its always good to let new chaeto adapt to your system slowly. Start with a small amount like a tennis ball or softball size chunk and let it grow. If you dump a giant bunch in at first, it can die overnight if your flow is slightly off or lighting isn’t powerful enough. A large amount of die-off equals a giant nutrient dump.
Failure to harvest. Chaeto needs to be harvested regularly. If you let it grow out without pruning it back, dead spots will develop in the centre where detritus can collect. An anaerobic nightmare. Plan on harvesting and removing 20-30% of your chaeto every other week to maintain proper growth rates.
Too much flow. Yes, opposite of not enough flow. If your chaeto is constantly in a stream of fast moving water, it will literally tear itself apart. Place chaeto refugiums away from direct output of powerheads or the flow coming from your return pump.
Expecting instant results. I can’t stress this enough. Chaeto takes time to establish in a new tank. 4-6 weeks before you’ll really see nutrient export and benefits to your system. Be patient and keep up water changes and maintenance as normal. You’ll begin to see your nitrates drop after about 6-8 weeks of steady growth if your chaeto is receiving enough light.
## Real-world Applications and Evidence
Chaetomorpha algae has been used in commercial aquaculture applications for decades due to its reliability and ease of growth. If you’re wondering how well chaeto works, large fish farms are using it to filter their water right now!
Chaeto can be extremely useful for nano reefs due to its dense growth habits. A handful of chaeto in a hang on back refugium can often provide the same amount of biological filtration as an expensive protein skimmer.
Chaeto doesn’t just benefit coral reefs. Fish only tanks can use the algae for filtration and pH stabilisation. Because there are no corals to feed, fish only tanks require more feedings which makes chaeto’s direct nutrient uptake even more valuable.
People use chaeto refugiums to breed copepods and harvest them for their marine fish fry food. Its no secret live food is the best food we can provide our fish. Having a refugium easily creates live food for your fish while stabilising your system.
I have friends who use chaeto in brand new quarantine tanks as a way to add some biological filtration without introducing mature filter media from another tank. They plant the chaeto, let it grow for a month, and then dump the whole thing after quarantine is over. No concerns of cross contamination between tanks.
## Benefits of Using Chaeto
Actual Nutrient Reduction: Chaeto doesn’t just process nutrients from your water, it exports them from your system. When you harvest your chaeto and remove it from the tank, you are permanently removing nutrients your tank didn’t have before you added fish or started feeding.
Chaeto can create day and night pH stability in your aquarium. By keeping pH swings to a minimum your livestock will experience less stress. Many reef aquarium keepers begin to notice improvements in coral colouration and polyp extension within weeks of adding chaeto to their system.
Natural Food Source: Refugium chaeto creates a habitat for copepods and other microfauna to thrive. These hyper-small creatures help to feed your fish and process leftover food or detritus in your aquarium. Many people pair chaeto with a BRS fish pods reactor to easily harvest pods to feed their fish.
Chaeto can also act as a backup filtration method. If your protein skimmer busts or your canister filter clogs, your chaeto is building more biodiversity inside your tank to help keep nutrients in cheque while you repair equipment.
Cheaper Than protein skimmers: Sure there are cheaper filtration methods than buying a refugium setup, but none as cost effective as chaeto. After your up front costs, chaeto only costs you electricity to run. No buying filter media, no replacing socks or filters.
Balances Your System: Think of a mature chaeto refugium as another layer of biological filtration. More filer spread across multiple methods makes your entire system more stable and resistant to crashes.
## Resources
* Aquarium Co.uk Forum Tips
* Saltwaternutrients Discussions
* Guide to Chaeto
* How to Grow Chaeto
* Aquatic Community Complete Guide
* SaltwaterREEF Advanced Guide
* Pro Tips from Reddit
* Reef Critters Macro Identification
* Nutrient Export Chaeto Growing
