When people think planted tanks, they automatically assume freshwater tanks with carpeting plants and CO2 dosing. However, there is a whole world of marine planted aquariums that I knew nothing about until I decided I wanted one too. Expect to unlearn everything you know about freshwater plants when keeping marine plants.
Marine “plants” are generally not plants at all. Many of the true marine plants are seagrasses, and they’re notoriously difficult to keep healthy and vibrant inside the home aquarium. The macroalgae commonly used for marine planted aquariums, however, provide the look you want while actually helping your water parameters in ways that benefit your fish and coral.
Salinity drastically changes the game as well. Saltwater at 1.026 sg (35 ppt ( Aquifarm), or parts per trillion) is a completely different environment for plants than freshwater. Just like everything else about marine planted tanks, don’t expect what you know about freshwater planting to work in saltwater.
## How Marine Plants Work
Saltwater Plants are Macroalgae
Chaeto is macroalgae, literally just giant algae. They won’t attach to rocks and decorations the way you may think of freshwater stem plants doing. They grow floating in the water column or attached to substrates, rocks, or structures in your aquarium.
Macroalgae differ from seaweed because they are cultivated and harvested regularly to prevent them from overtaking the aquarium. As live aquaria keepers, we are adept at growing things we shouldn’t be able to grow. With macroalgae, you want to grow lots of it to use as a natural nutrient exporter.
Proper Marine Planted Tank Lighting
It also does not take very intense lighting to grow macroalgae. Because they do not require as intense of lighting as corals do, stocking your aquarium with macroalgae can be a beautiful way to provide some plants without needing intense lighting. Macroalgae such as chaetomorpha or caulerpa can thrive on moderate lighting.
What Plants Do You Need?
Typically Chaeto, Caulerpa, and red macroalgae species. You want algae that takes up nutrients and helps clean the water like chaetomorpha would.
Chaeto (Chaetomorpha spp.) is one of the most popular macroalgae for nutrient export because it grows extremely quickly and can be harvested several times per month. It grows in long strands that look like stringy moss or brown thumbtacks.
Red macroalgae species include many options, such as green slipper lobster favourite Gracilaria sp. This macroalgae grows in bushy clumps that resemble miniature hedgehog corpses. It’s relatively easy to find and very hardy, making it a great beginner species.
Caulerpa can go sexual in your aquarium and actually kill your tank. It also releases toxins into the water column when it dies. While it’s a popular choice for aquarists due to its many varieties and low cost, I do not recommend it for newbies.
You Don’t Need CO2 Injection
In freshwater planted aquariums, we pump CO2 into the water to help plants grow. But because marine plants are mainly macroalgae like chaetomorpha, they don’t need CO2 injected into the water column. In fact, they will drop the pH drastically if you do.
Mistakes I Made
Chaeto doesn’t grow emersed from rock work like many freshwater plants. It grows submerged in the water column unless you glue it down or use fishing line to attach it to something. Caulerpa will attach to rocks decently but can also float in the water column if not secured.
Saltscape did an entire post about reef safe lights vs macroalgae growth (Saltscape). The LED strips I purchased to go under my rock work for freshwater plants were not heavy enough in the red spectrum to grow marine plants.
I bought a pound of macros because that’s how much the LFS wanted me to buy. A golf ball size chunk of Chaeto is more than enough to begin stocking a 200 litre aquarium. Macroalgae grow extremely fast under the right conditions. Add a couple ounces and watch it double in size every week or two.
When macroalgae are left unchecked, they can overgrow your aquarium. But because they consume nutrients from the water column, they can also consume so many nutrients that your coral begins to starve. On top of that, many types of macroalgae can reproduce sexually when they outgrow their boundary, poisoning your tank.
Just like you have to prune your freshwater plants, you will need to harvest your macros regularly. Once they’ve grown enough to be established, you should harvest about half of the biomass every two to three weeks.
My red macroalgae would not stay attached to my rocks. After doing some research, I learned that my flow was too strong. Once I slowed it down, they attached perfectly. Conversely, my chaeto died in one spot of the tank because there was not enough flow. It can take some trial and error to find the flow sweet spot for your macros.
Science behind Marine Plants
Different Flow Needs
If there’s not enough flow, detritus will build up around your macroalgae and limit its growth. Your macroalgae also won’t get enough nutrients transported to it at optimal speeds.
Too much flow can also be detrimental. Your macros can become detached and float away, or they may not receive long enough periods of light to photosynthesise properly.
You Need Reverse Photoperiods
The goal is to have photosynthesis happening 24 hours a day, somewhere in your aquarium. If your lights are on in the main display, the corals (and any algae) are photosynthesising. When your lights turn off at night, the refugium macros take over.
The refugium lighting I use is on a 14 hour timer. It runs from 7 pm to 9 am every day. This way, if my_main tank lights are on 9-7, photosynthesis is happening at all times somewhere in my system.
Live Rock and Substrate
You still want plenty of live rock in your aquarium. A good rule of thumb is 1-2 pounds of live rock per gallon(Reef Tank Resource). You also want at least 1-2 inches of sand bed depth (Bulk Reef Supply). Deep sand beds are nice because they create an anaerobic layer which helps denitrification. However, they can also create deadly hydrogen sulphide if not tended to properly.
Substrate Depth
The depth of your substrate doesn’t matter too much for marine plants. You can grow chaeto hanging off of rock work if you don’t want to deal with sandbeds. I prefer at least 2 inches of aragonite sand because it providesbeneficial bacteria surface area and help buffers my water’s alkalinity.
BUT if you don’t want to mess with sand, you don’t have to!
What Research Says About Marine Plants
Research from commercial marine aquaculture where macroalgae are grown on farms shows you don’t need fancy equipment or exotic lighting to grow marine plants. Just about anyone with a consistent light timer and basic macroalgae species can grow macros.
Research also supports that refugiums on reverse photoperiods can help stabilise pH by ensuring photosynthesis is happening at all times. Algae and corals photosynthesise during the day when the lights are on. Macroalgae in your refugium photosynthesise at night when your display tank lights are off.
Studies have been done on nutrient export via macroalgae and the consensus is that macros are very efficient at removing nutrients from your system. Chaetomorpha, in particular, has been studied numerous times and shown to export nitrates effectively.
Many aquarists prefer using macros to chemical methods of nutrient export. If maintained properly, a refugium can completely eliminate the need for chemical filtration.
Macros Across All Aquarium Types
Let’s discuss different aquarium types and how you can use marine plants to your advantage.
Large Reef aquariums
These guys benefit the most from dedicated sump refugiums. Your sump is essentially an extra aquarium where you can grow all the macros you want. These require separate lighting, so budget £300-500 to get things started.
Small Reef aquariums
Nano reefs ranging from 40-100 litres do fantastic with HOB refugiums or simple chaeto reactors. Budget £150-250 to equip your smaller system.
Fish Only Marine aquariums
Fish only tanks with rocks still benefit from macroalgae. The benefit is still there, you just don’t need as much light. Some aquarists actually prefer running refugiums with fish only systems because they don’t have to compensate for coral photosynthesis during the day.
Lagoon aquariums
A lagoon style aquarium is when you keep your macroalgae in the display tank. This is often referred to as a display refugium. This looks extremely natural and creates a lush habitat for your fish.
Benefits of Marine Plants
Stable Parameters
Macros can completely eliminate the need for chemical methods of nutrient export. Your nutrient levels will more than likely never be 0 but macros can reduce them to the point that dosing becomes necessary to keep levels from getting too low.
Many reef keepers dose NPK because their refugium is too efficient at exporting nutrients. Your corals need nutrients to survive as well.
Balanced pH
If you run your refugium on a reverse photoperiod like I mentioned above, you’ll never have to worry about pH swings in your aquarium again. When your lights are on, photosynthesis is happening in your tank maintaining a high pH. At night your refugium kicks on and does the same thing, balancing out your pH throughout the day.
Many people experience less pH swings in their aquarium when using a refugium. During the day, pH will rise as your corals and aquarium algae consume CO2. At night time when the fish are feeding and plants aren’t photosynthesising, pH will dip.
A refugium will keep it as stable as Mother Nature’s oceans.
Natural Look
Aquariums with macroalgae just look more natural than a plain fish only tank. Even if you’re not keeping any shrimp or inverts, macros add life and movement to an aquarium.
Easier Maintenance
Once established, you won’t have to worry about replacing chemical media or filter socks. You’ll simply harvest your macros and be set until they grow back.
Step by Step How to Setup Marine Plants
When to buy your Marine Plants
Phase 1: Purchase your lighting and macroalgae after you have your tank set up. Waiting to buy your livestock until the aquarium is cycling gives you plenty of time to research your lighting and equipment needs.
What you need for Marine Plants
* Refugium LED light: £80-150
* Small pump: £40-£80
* Timer: £15-£25
* Refugium chamber or HOB refugium: £50-£120
Total: £185-£375
When to Setup Marine Plants
Phase 1: This phase doesn’t actually take place until week 3 or 4. You’re not going to buy any livestock until your tank has ciclied. Use that time to research what types of macros you want, what lighting you’ll need, and how you want to build your refugium.
Phase 2: After you purchase your equipment and macros, it’s time to setup your refugium and begin stocking it with marine plants. This should take about a month to get established.
Phase 3: Macroalgae grow extremely fast. You may not even get to this phase. Once you see healthy growth and it’s covering the rocks/deco you put it on, you can begin harvesting.
Phase 4: Depending on the types of macroalgae you choose, you may need to tweak lighting times and flow rates. Not all algae like the same conditions. This is also the phase where you add more macros to your collection.
I hope this helps you decide whether marine plants are something you’d like to keep in your aquarium. Don’t be afraid to try something new and expand your aquarium hobbies beyond fish and coral. Plants are just as rewarding and provide benefits you never thought possible!
