Sunday, October 25, 2015

Marimo (Aegagropila linnaei) Care


Marimo, sometimes called moss balls or marimo balls, are a popular aquatic pet. While not an animal, many people keep them as pets due to their cute nature and easy care. Marimo aren’t a plant either. They are made of a type of cladophora algae that is rolled into balls by wave action (or by hands in captivity).  This algae is very slow growing and will not spread to the rest of your aquarium. They grow approximately 5 mm (0.2 in) per year, so there is not threat of it taking over your tank.

Marimo can live for a very long time. They grow continuously and at the same rate. The largest marimo is 95 cm (37 inches) in diameter. Given their growth rate, it is over 200 years old. Most marimo in home aquaria only reach 20–30 cm (8–12 inches). You can find them sold anywhere from 5 mm (0.2 in) up to 10 cm (4 in). The larger the ball, the more expensive it will be.

Giant marimo on display at Lake Akan (

In the wild, marimo are only found in lakes in higher latitudes. Colonies are known to exist in lakes in Japan, Scotland, Iceland, and Estonia. Two lakes in which they occur—Lake Mývatn in Iceland and Lake Akan in Japan—are protected by law. The colonies in Lake Akan are known to grow the largest and most rotund marimo. They live between 2 and 2.5 m (6.5 and 8 feet) deep where gentle wave action turns them over, keeping their cute ball shape.

Marimo are not the only form of Aegagropila linnaei. It will grow on the shaded side of rocks in an epilithic form or free-floating filamentous form that can form a carpet on the muddy lake floor. When small filaments of the algae get rolled into balls, they take the marimo form. These balls do not have a hard center and are algae all the way through.

Minimum tank size

Marimo necklace (SewOeno @ Etsy)

As long as the marimo is covered in water, the tank size doesn’t matter. Nano marimo (5 mm or smaller) can actually be housed in containers small enough to hang around a necklace. As the marimo grows it will need a larger container. You don’t even have to keep them in traditional aquariums with filtration as long as you change the water periodically. Water movement is also not necessary.  Decorative vases can be used as well as mason jars or anything that holds water. They can be kept in closed jars as long as you open the top every once in a while to let some fresh air in.

Temperature Range

Coming from high latitudes, marimo prefer cooler temperatures. They can handle temperatures up to about 78F (25C). Above that their growth can be affected or they can fall apart. When the water temperature begins to get this high, consider moving your marimo’s home to a cooler part of the house and change the water more frequently. Even though they come from cool lakes, marimo cannot take freezing temperatures. Protect them from frost.

Water Quality

Unlike fish whose waste products (carbon dioxide and ammonia) are harmful to their health, marimo’s waste product (oxygen) isn’t harmful. But they do need periodic water changes to replenish the minerals in the water taken from photosynthesis. It is also recommended to change the water more often in the summer to help keep the marimo cool.

When you change the water, you should remove the marimo and give it a gentle rinse in cool water. This will wash away any particles that may have attached to it. Roll it gently in your hands to help it maintain that cute ball shape. 
Marimo are unfussy when it comes to water parameters. A pH between 6 and 8 will suit them just fine. They will grow and flourish in just about all levels of water hardness. Interestingly, they can also take brackish water (to learn more about brackish aquariums read this article). In Lake Akan in Japan the filamentous form grows abundantly where salty water from natural springs flows into the lake. Sometimes a pinch of salt will help marimo recover when they have brown spots.


Marimo are algae, and algae operates much the same way as plants. They get their food from the sun. The only thing you need to give your marimo is light. A simple desk lamp will do. Indirect sunlight like that from a north eastern window (in the northern hemisphere) is good. Avoid long hours of direct sunlight as marimo can get too much light.


Any type of substrate is fine for marimo. People keep them on everything from sand to bare-bottom tanks. However, some people have found sand can get tangled in the threads of algae. I had a similar experience with my marimo and sand, and now I use large gravel or bare-bottomed tanks.

Tank Mates

Given the right-sized aquarium almost any fish makes a great companion for a marimo. Fish that eat algae like plecos, mollies, and hillstream loaches will not make good companions because their grazing on the marimo will likely outpace the marimo’s growth. The few fish that require temperatures regularly over 80F like discus will also be a poor choice for a marimo.


These beautiful golden fishies are often seen with marimo but not always in proper homes. Despite what seems to be everywhere, goldfish do not belong in bowls. You can read more about why they don’t belong in bowls in my goldfish care article. Even when placed in a large enough aquarium, goldfish aren’t the best companions for marimo as goldfish are known plant-muchers. They love soft plants and algae. Marimo are usually at the top of their list. Most goldfish will tear apart marimo. There is the odd case where a goldfish doesn’t eat a marimo, but why take the risk?
My marimo wrapped in twine to regain their shape after they lived in the goldfish tank.

Betta fish

Sometimes known as Siamese fighting fish, these little beauties are another common marimo companion. Like goldfish, they are often put in bowls but are not happiest there. You can read about why in my betta care article. Betta are another iffy choice for marimo as their temperature ranges only overlap a bit. Some people claim it doesn’t matter for the marimo, but others think it does. It might depend on the marimo. Some can take the warmth and others can’t. If you do choose a betta to be your marimo companion, be sure to have a backup plan in case your marimo can’t take the heat.

Good fish choices

Now that I’ve established some not so great fish choices, I’m going to give you a few species of common fish that have a better potential to work with marimo as they like the same cooler water and won’t munch on marimo. All of these fish need an aquarium larger than 10 gallons, and some will need a larger tank. For groups of fish fish look into zebra danio, neon tetra, glowlight danio, guppies, and white cloud mountain minnows. These fish are shoaling species which means they need to be around 6 or more of the same species. For a more solitary companion an axolotl is a good choice. They are actually a salamander not a fish, but they like the same low-light, cool conditions that marimo thrive in. You should research the needs of any fish you decide to keep with your marimo.


While shrimp eat algae, marimo are not on their dinner menu. Red cherry shrimp and ghost shrimp are two of my favorite shrimp commonly available. As their name implies red cherry shrimp are more vibrant than ghost shrimp. But red cherry shrimp will breed and may overpopulate a small tank. Ghost shrimp are much less likely to breed. They also grow larger than red cherry shrimp. Both shrimp love to graze on the bits and pieces that get trapped on a marimo and make great marimo companions.  

Red cherry shrimp cleaning a marimo (RW Sinclair on Flickr)


Another good choice for marimo are snails. These invertebrates eat algae but again marimo are not on their menu. Small snails like pond snails, ramshorn snails, and Malaysian trumpet snails do well in small tanks with marimo. Large snails like apple snails, mystery snails, and rabbit snails will need an aquarium larger than 5 gallons as well as supplemental food. Unlike the small snails, large snails can’t survive on the bits and pieces of debris around the aquarium.

Interesting Facts

Ceremonial returning of marimo to Lake Akan
Marimo are of great cultural importance in Japan where they have been declared a national treasure. Their name comes from the Japanese language and means “bouncy water plant.” When they were declared a natural treasure in 1921, people came from all over to collect and sell them as souvenirs. As a result the population in Lake Akan declined. It was dealt a further blow when a hydroelectric power plant was built along the Akan River which flows from the lake. The level of the lake dropped and hundreds of marimo were left stranded and dying in the exposed shoreline.

The local people recognized the treasured marimo was in trouble and launched a massive effort to protect them. An appeal went out to the people of Japan to return their marimo to the lake, and they responded in droves. The locals were so overjoyed by the effort of the people of Japan that they held a festival to celebrate the generosity of the people. The three-day annual marimo festival continues to today in Hokkaido.  One of the popular items in and around Hokkaido is an anthropomorphic version of marimo called Marimokkori. San-X also created Marimoko, a smiling plushie marimo.

Around Lake Akan there is a famous legend about the origin of marimo. It says the daughter of a chief of a powerful tribe living on the banks of a lake fell in love with a commoner, but her parents objected to the relationship. To be together, the couple gave up all of their possessions, ran away together, became marimo, and lived happily ever after. For this reason, marimo symbolize love in Japan and are often given as gifts to loved ones. It is believed that if you take good care of a marimo, it will bring you happiness and good luck.

Works referenced

"Marimo and Lake Akan." Japan Atlas. Updated: 20 Febuary 2013. Accessed: 25 October 2015.

"Marimo Balls." Aquariadise. Updated: 13 May 2013. Accessed: 25 October 2015. 

"Marimo Care." Buy Marimo. Updated: 2014. Accessed: 25 October 2015.

"What is a Marimo." Marimo Sanctuary. Updated: 20 October 2015.  Accessed: 25 October 2015.

**Disclaimer** Since there is little to no scientific research about fishkeeping published, much of the hobby today is opinion, but they are opinions given by keepers and breeders who have been doing this longer than some of us have been alive. Temperature ranges and adult sizes are not opinion. They have been scientifically documented.

Sunday, October 18, 2015

Freshwater Aquarium Nitrogen Cycle

Welcome to the most important article I or anyone can ever write about fishkeeping: the aquarium nitrogen cycle. Contrary to what you may hear at a pet store, it is not just filling your aquarium and running the filter for a week.

What Is It?

The nitrogen cycle is how we maintain a healthy environment, and it surprisingly relies completely on bacteria. These microorganisms change the toxic waste of our fish into a relatively harmless substance, thereby allowing us to keep fish in contained areas. In the wild, the fish waste is diluted by the humongous volumes of water. 

The cycle begins with fish. They produce ammonia as a byproduct of their metabolism. The problem is ammonia is toxic to them (and us for that matter). Luckily a genus of bacteria called Nitrosomonas exists. These bacteria take ammonia and convert it into nitrite to generate energy for themselves (much like plants use photosynthesis to generate energy from the sun). However, nitrite is still toxic to fish. That’s where second genera of bacteria called Nitrobacter and Nitrospira come in. They convert the toxic nitrite into nitrate which takes much higher levels to reach toxicity. However, nitrate is still toxic to fish and will need to be removed from the aquarium by its caretaker. This is one reason we perform periodic water changes on our aquaria.

Aquarium nitrogen cycle schematic. (public domain)
Nitrobacter and Nitrosomonas also have requirements just like our fish. They live on surfaces in your aquarium although a small amount can be found floating in the water. They operate best between the pH’s of 6.0 and 9.0 and need water above 50F. They also require highly oxygenated water, so they are most commonly found in the filter. For this reason, it is important to never wash your filter media in chlorinated water. 

When plants are added to an aquarium, they use up nitrogen in all three of the forms (ammonia, nitrite, and nitrate). If enough fast-growing plants are present, there may be very little ammonia that makes it to the filter. However, even with a planted aquarium, I recommend having some type of filter where these important bacteria can grow. Plants can be finicky and stop growing for odd reasons, and when that happens an ammonia spike can be deadly to fish and invertebrates. Having plants does not negate the necessity of the nitrogen cycle in your freshwater aquarium.

How to Establish a Cycle

Cycling an aquarium takes weeks to a month because the colonies of bacteria replicate slowly. Nitrosomonas need a source of ammonia to produce nitrite before Nitrobacter can begin to grow.  The only way to know when it is complete and what stage you are in is to test for ammonia, nitrite, and nitrate. First you will see an ammonia spike, followed by a nitrite spike, and then nitrates. You should test your water daily and record your results to chart your progress. A few different methods of getting ammonia into your aquarium and starting the cycle are detailed below.

Chart of expected ammonia and nitrite spikes while recycling a tank. (

Live Fish

This is the most common and oldest method. Simply throw the fish in and hope for the best. The bacterial colonies will build up over time, but while you are waiting your fish will be subject to ammonia poisoning and nitrite poisoning in the weeks it takes the Nitrosomonas and Nitrobacter colonies to establish themselves. This is how many ignorant aquarists (including myself) originally establish a cycle, however it is not the most humane. Other alternatives should be explored first. 

Fish Food

In addition to living fish producing ammonia, decaying food will also produce ammonia and can be used to start a cycle. You can use fish food or raw seafood. However, this method isn’t without risks as rotting food will attract other bacteria and fungi. If you are using this method, you need to do a large (70% or more) water change before you add fish and invertebrates. 

Pure Ammonia

You can find this sold as a cleaning agent in many stores. Just make sure you check the label because the ones with surfactants will not work. Add the ammonia to your tank water until you get a concentration of 3ppm (any higher and it will inhibit the Nitrosomonas). When the ammonia concentrations drops to zero and you see nitrites, add more again. Keep doing this until adding ammonia produces nitrates. You will have to keep dosing the tank until you add fish to sustain the colonies. Before you add fish, do a water change to reduce the nitrate levels to below 40ppm. 

Seeded Filter

If you have a friend or store you trust, you can ask for some of their filter media to add to your filter. Because these bacterial colonies are most commonly found attached to filter media, you will instantly establish a cycle. You can add fish the day you add in the media. If you have multiple tanks you can borrow media from one tank to cycle another. Since I cycled my first aquarium, I have used this method exclusively to cycle my tanks. 

Bacteria in a Bottle

Nitrosomonas and Nitrobacter can be bought from pet stores and online. A few select products are believed to work quite well. Dr. Tim’s One and Only and Tetra Safestart are two that are claimed to work wonderfully. By adding these products you can cycle your tank instantly and add fish that day. You can also use these products in conjunction with any other method to increase your chance of success. I have not personally used these products at the time of writing, however I have heard amazing reviews from others. I do have plans to try these products myself one day.

Cycling an aquarium is the single most important thing you can do for the health of your fish. It is time and effort, but it is worth every minute for the headaches it will save you. The best medicine is clean water, and that is just what a cycle gives you.

Works Referenced

Ammonia & the Nitrogen Cycle: Important Steps for YourAquarium.” Drs Foster and Smith. Updated: 18 October 2015. Retrieved: 18 October 2015.

Aquarium Nitrogen Cycle.” Fishlore. Updated: 30 September 2015. Retrieved: 18 October 2015. 

DeLong, D.P. and T.M. Losordo. 2012. "How to Start a Biofilter." Southern Regional Aquaculture Center. Retrieved: 18 October 2015. 

Fishless Cycling.” Algone. Updated: 15 March 2012. Retrieved: 18 October 2015. 

’Fishless’ Cycling.” The Skeptical Aquarist. Updated: 21 March 2011. Retrieved: 18 October 2015. 

Helm, Ben. 2014. “Controlling Ammonia in a Fish Aquarium.” Retrieved: 18 October 2015.

 Losordo, T.M., M.P. Masser, and J. Rakocy. 1998. "Recirculating Aquaculture Tank Production Systems: an overview of critical considerations." Southern Regional Aquaculture Center. Retrieved: 18 October 2015. 

Monks, Neale. 2011. “FishlessAquarium Cycling Method.” Retrieved18 October 2015. 

Nitrifying BacteriaMixtures Work.” Dr. Tim’s  Aquatics. Updated: 8 September 2015. Retrieved 18 October 2015.

Sunday, October 11, 2015

My tanks: 11 Oct 215

I'M BACK! Since it's been over a year, lots of changes have happened with my tanks. Fish have come and gone. I'll try to remember to say what happened to all of my projects, but if I don't mention one feel free to remind me!

The biggest change that happened is I moved to Georgia for graduate school. This means I had to leave my pond back in Virginia. It is in good hands, tho. My mother still resides in the house and has been taking care of it and keeping me updated. I periodically return especially around the holidays, so photo updates will still come in for the pond.

Even before I moved to Georgia, all of my betta fish died, and I did not replace them with more. Betta are beautiful, but they are so fragile. Fall of 2013 the two betta in my divided tank died after contracting what I believe was lymphocystis from the pet store.  They were both plakats and very beautiful, but I think if I return to betta fish it will be the wild Betta spp. I do plan to keep up my betta care sheet and quick reference page as betta are very popular fish in the hobby.

While my betta did not make the trip with me to Georgia, my goldfish did. However, due to the stresses of grad school, I was unable to give them the care they needed. One succumbed to bad water quality before I realized what had happened. I gave away the other. Unfortunately Mr. Waddles, my rescue, died before I moved, most likely due to issues with his tank before he arrived at my house. I don't see myself returning to goldfish keeping any time soon, but I will continue to update my goldfish care sheet because they are such an misunderstood fish. The more misinformation I can correct, the better.

Last but not least (I do still have ONE tank) is the 29 gallon community. I still have my adorable loaches. They happily made the trip with me to Georgia. A few cardinal tetra did, too. An accident with dechlorinator was their end. Let this be a lesson to everyone: always add dechlor before you add water back into the tank.

Current state of the 29 gallon. Plants are mostly low-light. Filter is a Finnex P-360

However, you may notice there are still little tetra swimming around in the 29 gallon. Recently I got a different species of tetra to fill the upper spaces of the tank. I opted for glowlight tetra (Hemigrammus erythrozonus) due to their hardy nature. They are commonly recommended for beginners due to their forgiving nature, and I've always thought they were pretty. So I wanted to try them out. I received 10 of them and have already been smitten by them. They are surprisingly easier to photograph than my cardinals were. It probably also helps that I got a new camera, too.

Glowlight tetra (Hemigrammus erythrozonus)
And a shot of my loaches because I love them too much not to include them! ^-^

So those are all the changes that have occurred since my unplanned hiatus. I do not expect to be setting up any more tanks until I finish grad school, have a career, and a house. So future updates will be few and far between. 

Monday, October 5, 2015

Back again!

Hello everyone!

Thank you for holding on this long, but my unexpected hiatus is over. I'll be doing some updates on the blog in the coming weeks to prepare for a new theme (sort of). Links need to be updated and whatnot. I also need to update you all on my fish tanks! LOTS of changes happened there. I've also started grad school working towards an environmental education degree, so some of that may slip in with regards to fish.

so YAY I'm back :D

EDIT: I've also changed the url to fishgirlwrites! My old url will still be there to prevent any broken links!