Tiny Invertebrates in Tiny Tanks




Introduction: Tiny Invertebrates in Tiny Tanks

I've never had much luck keeping fish, but when my sister found some tiny swimming creatures in her fish tank along with her fish, I found those fascinating and wanted to learn more. She was glad to give these little guys a home with me rather than tipping them down the drain along with her water-change waste. She also had some extra snails for me to take.

To start with, I had a coffee jar full of aquarium water and I was feeding them on tiny scraps of lettuce. The creatures seemed to thrive and the population of tiny swimming specks grew and grew. However, planarian flatworms were also in the mix and, as I found out, they do a great job of fouling up their environment with slime.

The slime jar had to go.

I decided to set up a proper aquarium dedicated to these small-scale citizens of the aquatic world.

My first attempt turned out okay but the snail population got out of hand so I decided to set up a second tank for this instructable and do things differently based on what I learned the first time around.

Step 1: Obtain an Aquarium

The smaller the amount of water you have in a container, the harder it is to keep it in good condition - so I went looking for something bigger and more appropriate than the coffee jars I'd been using. I came across this corner tank for very cheap ($10) at a local store. The dimensions are 20cm x 20cm x 28cm tall, but since it's triangular the volume is halved. Assuming its not filled right to the top, it holds maybe a bit over 5 litres, or 1.5 US gallons? I certainly wouldn't want to keep fish in something this small, but it is perfect for the tiny creatures I want to keep.

I found later that the sharp angled corners were quite difficult to get my hand in to place plants and clean so keep that in mind when selecting your container.

However, the long side of the tank does provide a great flat viewing surface which has made observing the inhabitants a lot easier. The curved sides of the coffee jar made viewing very difficult so I would definitely recommend a flat sided container over a curved container when you are making your choice.

I liked this corner tank so much that I went back and got a second one for my second attempt. The viewing area is quite good vs the footprint it takes up on the shelf so I was happy to put up with the narrow corners.

Step 2: Prepare the Aquarium

I wanted to create a healthy environment for the animals that I was keeping so I bought some aquarium plants to provide oxygen and maybe food for the snails.

I wasn't sure what would work so I bought a variety of plants to see which were suitable.

Hydrilla - an alternative to Elodea since this waterweed isn't allowed where I live. This seems to grow reasonably slowly, and I can't see the snails doing too much damage to it.

Vallisneria Asiatica (Eel grass). The original Eelgrass plant I bought was fairly large and has since sent off lots of little shoots and runners. I used a small new plant in this aquarium, hoping that it wouldn't grow too crazy. The snails go up and down the long narrow leaves but I think they are eating what grows on the surface of the leaf, rather than the leaf itself.

Eleocharis (Hair grass). This grass grows in linked clumps and is very frustrating to try and plant without it sticking to your hand or floating away in the water! It looks nice though and I don't think it grows too fast. I was able to weigh it down with pebbles. The snails don't seem to eat it.

Ceratophyllum Demersum (Hornwort). This plant grows like crazy! I think it's too tough for the snails to eat although where it breaks the surface of the water it goes soft and perhaps the snails eat it then. On the other hand, it provides great cover and many places for small creatures to hide, also a lot of surface area for food to grow on. A small single piece of this will eventually multiply and fill up the whole tank so don't use this unless you're happy to keep up with the pruning. The snails like laying their eggs in it, too.

Myriophyllum papillosum (Common Water Milfoil). This plant grows long curling stems with fine delicate looking leaves. I think it grows too tall for the tank that I am using and it doesn't provide as much cover as the Hornwart. The leaves are quite pretty though. It could work if you are using a tall tank but I think I will use this plant in my pond outside rather than in the aquarium.

Rotala Rotundifolia. The snails love munching on the leaves of this plant, however I think they only eat the brown/dead leaves and are leaving the new green growth alone. It doesn't seem to grow very fast and it has pretty flowers.

Java Moss. Seems to grow in a fine tangled mess of branching stems with tiny leaves. It provides a lot of surface area which is great for foraging critters. It does grow a little fast though so monitoring and pruning will be required.

All of these plants are considered to be appropriate for aquarium use, and are fine with low light levels. When I started out, I didn't plan on buying specialised aquarium lighting so I made sure to choose plants that could handle less light.

Note - check whether your chosen gravel/sand/substrate for the bottom of the tank needs to be washed before use. The one I used needed to be washed and also soaked in water to stop it from floating away. I used a plant-friendly substrate in the very bottom of my tank, and placed my chosen plants into position before adding the water. I put a layer of polished stones over the top of the substrate to help keep everything in position. Then, I added my prepared water very carefully and slowly to the tank. Depending on your conditions you may need to treat your water to make it safe for aquarium use.

Let your tank sit for a while before adding anything, give the plants a chance to settle in.

Step 3: Other Equipment You May Wish to Use


I had some USB powered monitor bias lighting laying around that I wasn't using - you're supposed to stick the strip of LED lights to the back of your monitor so that it shines at the wall and that reduces eyestrain by evening out the glare. The strips were never really sticky enough to stay stuck where they were supposed to and and I used masking tape to attach them to the rear of my tank. If you have a lamp or some other kind of lighting you wish to use, it does make seeing what's going on in the tank a bit easier especially if the light is behind the side that you're viewing from. I did end up buying a cheap LED plant lamp as well but the plants, especially the hornwort, were doing okay without it. I put it on a digital timer to run during the day and turn off at night.


After seeing how slimy a jar of still water could get, I wanted to find a way to get a bit of movement in the water. However, the lowest powered water pumps I could find still agitated the water far too much and the moving parts of the pump seemed to me to be too dangerous for the small swimming creatures, which would easily get sucked in to the impellor. So as an alternative, I bought an air pump, airstone and some tubing, T-pieces, air control valves, and a check valve. I also bought a sponge filter that was suitable to be powered by air - these are sometimes marketed as fry-safe filters. If you don't want to buy one of these filters you can DIY - for example this instructable Air Driven Filter by rgrling is a good starting point. If you're buying one check that the dimensions are suitable for the size of the tank you've chosen since the sponge filter might take up more room than you expect. In my second tank, I am seeing how it will go with just an airstone and no filter.

Put a lid on it

The corner aquarium did not come with a lid, so I cut one out of corrugated plastic. I have cats and I would rather they did not drink out of these tanks, both for their own safety and the safety of the tank inhabitants. It's possible for snails to carry flukes which can cause diseases if passed on to your other pets, whether they are cats or fish. Always wash your hands after handling aquarium water.

Step 4: Stock the Tank!

I was lucky and was able to get some interesting creatures from my sister's existing aquarium. Every time she uses the gravel cleaner and does a water change, she sucks up many organisms along with the fish waste. However if you are not lucky enough to know someone who could provide you with some starter creatures, you do have other options.

Quite often when you get aquarium plants they will come with hitch hikers. I obtained ramshorn snails and hydras from one of the plants I bought. The ramshorn snails brought along some friends too, tiny commensual worms which hitchhike on the snails and grab even tinier creatures from the water.

Another place you might find interesting small invertebrates is if there is any still or running fresh water nearby. I was able to catch some daphnia (water fleas) and a different kind of copepod just by dipping a jar into the water. You might have better luck using a net made out of pantyhose.

My original tank contains:

Pond snails

Ramshorn snails







Insect larva (I think its a moth fly larva)

and probably more things that I can't identify. I made sure not to transfer any planarians out of my original jar though, those guys are just too messy for my liking.

My second tank has a single ramshorn snail and I transfered some copepods and ostracods to it.

Step 5: How to View the Inhabitants of Your Tank

You might have noticed at the start of this instructable I was a little bit coy about what exactly the animals were that I was keeping in the aquarium. The truth is, I didn't know myself until I was able to observe them up close, to identify them.

You should be able to see your snails and your largest crustaceans with your naked eye, however the best details are observed via magnification.

I was inspired by Zephyris' instructable on creating a simple webcam microscope, however my old webcam didn't work once I'd got the lens out of it. I found I was able to just hold the reversed lens up to my eye and lean close to the side of the tank which let me see anything within a few millimeters of the glass. I was also able to use this lens held up against the lens of my phone/tablet's camera to film footage. There are fairly cheap macro kits available for most types of phone too and I think this would work under the same principle but as you can see, I got decent results with just the reversed lens. The hardest part is keeping everything steady while filming.

Step 6: How to Feed

What food to provide your tank will depend on the inhabitants of your tank.

Pond snails and ramshorn snails seem to like rotting plant matter and will eat added vegetables such as pieces of lettuce, broccoli, zucchini. They will devour fish food flakes if they get access to them but the more you feed them, the more eggs they'll lay and you'll soon have a runaway snail factory like my first tank became. So why have snails at all, you might be wondering? The answer to that is simply: many of the other things living in the aquarium will eat the snail droppings. They're a part of the ecosystem and to keep it in balance it is really important to not overfeed the snails.

Copepods are predatory and eat planktonic life, although they will eat plant debris as well. They are known to eat newly hatched mosquito larvae. Ostracods are omnivorous as well. In the case of these animals, you need to provide food for their prey rather than directly feeding them. I am currently using very small amounts of fish fry powder food but previously dried crushed lettuce and very very small quantities of baking yeast seemed to suffice. If you have hydras, they will also eat planktonic life, unfortunately they also eat copepods. When I set up my second tank I was very careful not to add any hydras along with the plants. I've heard that ramshorn snails will eat hydras but so far all I've seen is a snail bump into a hydra, the hydra retracts a bit and the snail pulls a face and glides away.

Insect larva might eat decaying plant matter, or algae, or they might be predatory and chase your other critters around. The moth fly larvae I have seems to hang around on the bottom eating gunge.

Another good way to provide food for the smaller organisms in your aquarium is to set up a "bioreactor" in a jar (I don't know what else to call it!). Get some straw or dried grass from your garden and boil it in water for 5 or 10 mins. This will help break down the cellulose. Let the water cool and put it and the grass/straw in your jar. The other things you'll need for this are light and air. I cut a hole in the lid of my jar, threaded an airline through it and then attached the airstone. The hole in the lid should NOT be airtight against the airline! Lastly I wrapped one of the LED strip lights around the jar. You could place it under a lamp. Before you seal the jar up, you need to seed it with some pond water, aquarium water or even water from a puddle outside. Set the airstone bubbling and put the lid on and let it go. After a few days the water will be colonised by rotifers, paramecium, bacteria, yeasts, maybe even amoebas all feeding on the cellulose you've provided them. With magnification you might be able to see a few of these creatures but they are very very small. You can then use water from this jar as a source of food for your aquarium.

Step 7: Safe Water Changes?

So far I haven't done any water changes as I don't want to suck up and lose any of the inhabitants of the aquariums. The biological load is fairly small but as the number of snails increases, the amount of waste they produce will build up. Since I set these tanks up I have read about the nitrogen cycle and I know with fish it's important to remove their waste products via water changes so I am assuming the same will be true for invertebrates (even tiny ones).

Most of the animals in the tanks can handle poor water conditions but I do not intend to let their water degrade to that point. I've been thinking it through and I believe it would be possible to use a sponge over the end of a siphon hose to prevent any unintentional abductions by suction. I don't know whether it would reduce the flow of the siphon a significant amount though. If it does, it might be possible to use the gravel cleaner that I already have, add a sponge up the end, and also add an airline to provide bubble suction power (similar to the sponge filter). It's definitely possible to pump water via air bubbles so this might get around the low flow of a simple siphon.

I might make a future instructable about this as I am now considering running an aquarium with shrimp in it, and water changing a tank with baby shrimp in it would a pose similar issue to my current tanks with their miniscule inhabitants.

Step 8: Things I Have Learned.

I had a great time trying to set up these tanks to observe and learn about the smaller forms of aquatic life. I hope anyone who reads this is encouraged to investigate these fascinating creatures too.

Before I started, I had no idea how fast snails were able to reproduce. If I'd have known I would have removed the snail eggs rather than letting them develop and hatch. By trying to do the right thing and add real plants, that made the job of keeping track of eggs much harder. Snails are apparently a constant problem with aquarium enthusiasts. They are surprisingly fun to watch though.

Another thing I learned was that ostracods seem to prefer still water to moving water and they seem to prefer dirty water to clean water. I found one of my original coffee jars that had lost much of the water due to evaporation, and it was absolutely teeming with ostracods. I've set up a separate tank for these ostracods with some hornwart and snails since they don't do as well in moving water. Paramecium similarly don't reach the same numbers in moving water as they do in still water, or perhaps they're all happily living in the sponge filter of that tank. Before I bought the sponge filter the water was cloudy with paramecium and it was amazing to watch them react to the lights by teeming and swirling in clumps. I tried to film it but it was next to impossible to get a video showing the effect. I guess the other thing could be there are too many predators now for the number of paramecium to build up that high.

Lastly, I've added a picture of the Hornwort and Water Milfoil that I trimmed out of my first tank. In a bit over a month there was well over a foot of growth from each! Both plants grow fast without special lighting, which might be useful in some aquariums but not a small tank like mine.

Thankyou for reading my first instructable! If you like, you can vote for me in the Age of Aquariums contest.

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    You did awesome your first time making an instructable! I love your little critters, I was always partial to brine shrimp myself. Thanks for sharing!


    Reply 3 years ago

    PS, I installed a strip of cardboard yesterday between the jars and the window. Hopefully that will reduce the algae explosion.
    Also, I had a jar with a dozen mayfly larvae. They were large enough for easy viewing, very active, and survived for more than six months (until my cat sent the jar crashing to the floor).


    3 years ago

    Nice one.
    I have a row of mason jars on my window sill, with a different population of tiny invertebrates in each. I agree that snails reproduce far too rapidly :)
    I do frequent water changes as the south sun causes the suspended algae to fill all available space, making it difficult to view the inhabitants (and I believe it impedes their movement, too). I use a turkey baster to remove water from the least inhabited (or most polluted) areas.


    7 years ago on Step 2

    Cool! I used to have a freshwater planted tank specifically to raise creatures like these. I had so much fun watching their behavior and trying to find out exactly what species were growing. Thanks for sharing all the info you have acquired. If you have access to outdoor ponds, you might want to catch a young drangonfly larva. I raised a couple to adults and they destroyed my snail population with their voracious predatory appetite. Keep it up!


    Reply 7 years ago on Step 2

    I'm still digging the hole for my back yard pond. Good to know that dragonfly larva will eat the snails, I know we do get big dragonflies in these parts and I intend to leave my ponds free of fish to allow local critters to move in. Last night I could hear frogs croaking from somewhere nearby even though we haven't had rain yet, so I'm hoping my pond will give them more places to breed.


    7 years ago on Introduction

    Water changes recommended in most aquarium forums are mainly used to to keep the dissolved minerals in balance in an aquarium. Every time you feed fish you add phosphorus, potassium , iron, calcium and other minerals. If you don't remove any of these minerals they can build up and eventually kill fish. water changes can also help remove nitrates and ammonia (although plants do a better job.. As to solid fish waist, water changes don't really remove it. Instead bacteria feed on the waist and eventually convert it to CO2, water and resolved minerals.

    I would not sugest using distilled water or RO (revers osmosis) water as part of normal water change routine. I did this on an aquarium I set up about a year ago an my plants didn't consistently grow and eventually died. However when I did a water change with Hard tap water (my RO system was down) The plants started to recover and grow. I eventually figured out that using RO water as part of my aquarium water cycle slowly depleted the calcium in the tank eventually killing the plants. I now cycle my aquarium with 50% RO water and 50% hard tap water. and my plants seem to do well.

    I also put some duck weed (a small floating plant) in my aquarium. As it grows it removes minerals from the water. Any excess I periodically remove. I believe this with a small water change will keep in the minerals in balance. If I have to add water due to evaporation I use RO water.

    As to what the snails eat. Yes they eat dying plant mater. But they also eat the bio film (bacteria, and algae) growing on plants, and gravel in the aquarium. Many people periodically clean the glass of there aquarium to remove the algae growing on it. I don't. My 3 Nerite snails keep the walls of my 5 gallon Aquarium clean and do a good job cleaning the gravel on the bottom of the tank. I don't feed them although any fish food that settles on the bottom is available to them. Nerites live in brakish and fresh water but can only reproduce in brackish water. So I am not worried about them taking over the tank.

    As good as the Nerites are in keeping the auqarium clean they cannot reach Algae growing on my plants (they are too big). I recently added one Amano shrimp to my aquarium and he appeas to have slowed down the growth algae on the plants.

    I will be adding two more. If that works I won;t have to worry about the hair and film Alge growth on my plants. Like Nerite snails Amano shrimp typically bread in brackish water. So hopefully I will not have to worry about a shrimp population explosion.

    The Copepods Ostracods in your tank are mainly filter feeders. They feed off of bacteria, perquisites, and bacteria in the water. they help keep you water clear.

    So if your aquarium has enough light and the minerals are in balance you might not need to feed your aquarium to keep them. I would avoid a water changes and just add RO water as needed to make up for evaporation. You might even be able to seal the aquarium to eliminate water loss.

    There are items called EcoSpheres that are sold (http://en.wikipedia.org/wiki/Ecosphere_(aquarium). It is basically an sealed Aquarium with small shrimp algae and plant. The shrimp eat the algae and algae live off of the waist from the shrimp. With luck you might be able to do the same with what you have now but with more diversity than the typical ecosphere.

    My goal with my aquarium is to minimize the need for maintenance. I am using plants to keep nitrogen levels under control and Nerite snails and Amano shrimp to keep most alea under control. So far successfully. If needed I may add Daphnia or clam shrimp (filter feaders to my tank if a grean water or perisite problem developes). Also note that there is a fresh water version of brine shrimp called fairy shrimp.







    Reply 7 years ago on Introduction

    That's an extensive and awesome comment and actually made me consider eventually getting a fish tank with the idea to balance it for minimum maintenance, thanks!

    And thanks to the author as well, the tiny living beings are sure an interesting concept.


    7 years ago on Step 2

    I forgot to mention the small piece of rinsed coral rock that I added. I had some small pieces that I'd collected at the beach and thought it would make a nice decoration in my first tank. The snails soon swarmed all over it which made me wonder if they were gnawing on it as a source of calcium - not sure if their mouth parts are tough enough to manage this! In any case it will act as a buffer against acidity in the water.