It's A Small World, Pico Tanks

By Kirby Adams

It’s no secret that things are getting smaller every day.  Walk into a technology store and you’ll see stereos that used to fill a room that will now fit in the palm of your hand.  Aquariums are no different.  Saltwater aquarists used to talk about "microreefs", which usually referred to tanks that were nothing short of enormous.  Then, during the last few years we’ve had an explosion of "nano tanks", popular among both freshwater and marine hobbyists.  Now we have the arrival of "pico tanks", topping out at about five gallons.  For metric system enthusiasts, the next three steps in descending order are: "femto tanks", "atto tanks", "zepto tanks", and "yocto tanks".  Let’s hope it doesn’t go that far, because I don’t want to try to find animals for my half-ounce "yocto reef"!

In the meantime, we have these "pico tanks" and we need to put something in them.  Tiny tanks offer challenges in several areas.  The first order of business is to figure out what kind of animals stay small enough to inhabit the tank.  After that we have to make sure we are able to maintain stability in such a small system.  Let’s work backwards and go over that second part first.  Then we’ll look at a few picotanks that would look great on your kitchen counter. 

When dealing with small quantities of water, it is important to remember that bad things can happen much more quickly than in larger systems.  A little overfeeding in a 75 gallon tank might not be a big deal, but will be deadly in two gallons.  Overdosing a chemical in a 180 gallon reef could be a minor problem but would cause complete devastation in a "pico reef".  So we want to be careful about stability and yet keep things simple, because this is supposed to be fun, right?  The first step to stability is a filter of some sort.  A sponge filter driven by an air pump or a hang-on filter with some type of biomedia is best.  The single most important type of filtration in any tank is biological filtration – the removal of toxic ammonia and nitrite by means of live bacteria and plants.  Sponge filters and biomedia are simply means of giving the bacteria a place to live where water will flow past, allowing them to do their detoxifying work.

The second step to stability is the good old-fashioned water change.  It’s the simplest and most effective means of keeping the chemical properties of the water in line.  On the "pico tanks" mentioned below, I recommend a 25% to 50% water change once a week.  As long as the water used is similar in temperature, pH, hardness, and salinity (in saltwater) a 50% change won’t be any stress at all to the animals.  While it might seem like a lot of work, water changes are really a breeze.  In "pico tanks", a water change might only involve a couple one-gallon jugs of water.   Using a half-inch diameter siphon, it will take less than a minute to remove the old water.  The whole process won’t last more than a few minutes.  Just like the regular oil change in your car, it’s a cheap and easy way to ensure a long and healthy life for your tank. <Editor's note- this is a great practice with ANY sized system!>

Now that we have a filter and we’re ready to do our regular water changes, let’s get down to the fun part.  There are hundreds of different things you can do with a tiny desktop aquarium.  Below, I’ve picked out four that should appeal to a wide range of tastes.  Half are marine tanks and half are freshwater.  All of them are guaranteed conversation pieces!    

Saltwater hobbyists often find themselves starting down the road to a reef tank with the addition of some of the colorful “Mushrooms.”  Some folks call them Mushroom Anemones and some call them corals.  They actually belong to a different group entirely, known as the Corallimorphs.  Known for hardiness, tolerance of lower light intensities, and preference for weaker water flow, they make excellent choices for the picoreef.  The four gallon reef tank pictured in this article is filled with different colors and varieties of mushrooms, with a few Zoanthids thrown in for spice.  A tiny fish like the Neon Goby or Green-Banded Goby adds some movement.  The mushrooms do not need to be fed directly, thus limiting the amount of food introduced to the tank to only what the goby requires.  The Mushrooms will feed on detritus and stray pieces of food. 

The same four gallon tank can just as easily be a freshwater planted aquarium, like the one pictured here. This tank is aquascaped with a simple piece of driftwood and the very hardy, dark green-leaved Anubias.  Several Glowlight Tetras provide the flash and movement in this tank.  The aquarium a bit more challenging by adding some of the slightly demanding plant Rotala sp. “Nanjenshan”, a plant native to Taiwan. Despite some of its touchiness with respect to handling, the plant has evolved to tolerate swings of temperature quite well. Aquatic plants can grow rapidly in good water conditions and the planted "pico tank" can require frequently pruning as it matures.

Sticking with freshwater, we could design a "pico tank" around one unusual animal.  The Wood Shrimp, also known as the Bamboo or Fan Shrimp, makes a fascinating subject for a desktop tank.  The most commonly available of these shrimp is Atyopsis moluccensis, an attractive and hardy species from Indonesia.  Wood Shrimp have evolved feeding appendages that open like fans to catch tiny food particles in the water.  If the tank is designed with a filter strong enough to generate areas of higher current in the tank, the wood shrimp will position itself in the current and open its fans, closing them one by one and pulling the catch to its mouth.  Adding to this odd behavior is the Wood Shrimp’s chameleon-like ability to change color.  Your shrimp might be brown tonight, golden yellow tomorrow morning, and bright red by dinner time!  Anyone who thinks all the interesting invertebrates live in saltwater need to check out the wood shrimps.  At four inches long, these shrimp push the limits of some of the tinier picotanks.  A four gallon or larger tank would be best, with strong current as mentioned above and adequate mechanical filtration since a four- inch shrimp eats a lot of food. 

Back on the saltwater side, we’re going to stick with the shrimp theme.  Our choice here is the outlandish looking Harlequin Shrimp (Hymenocera sp.)  Harlequins are a hardy shrimp often offered for sale as mated pairs and well known for their quirky eating habits.  They are obligate Starfish eaters!  The term obligate means they will not eat anything else.  Without live Starfish as a source of food, they will simply starve.  Some species have been reported to prey on the tube feet of Sea Urchins, but this is not common and not something that be offered regularly in the aquarium.  A source of live Starfish, conversely, is not as difficult to obtain as it would seem.  In the past, Harlequin keepers had harvested legs from Linckia stars or Chocolate Chip Starfish (Protoreaster nodosus).  This rarely worked for long, as the Starfish would suffer an infection and fail to regenerate a leg as hoped.  It is also irresponsible to support the harvest of delicate Starfish to be used as feeders when an easier alternative exists.  A majority of reef tanks will have at least a few of the diminutive Starfish known as Asterina.  These are small white to brown Starfish with variable numbers of legs that are found clinging to algae and bacterial film covered surfaces in any typical reef.  They reproduced rapidly and can become a pest in some heavily-fed systems.  Many stores are now offering Asterina for sale as food for Harlequin Shrimp.  Contacting other reef hobbyists through a local club or message board should get you several other sources for cheap (or free!) Starfish.  Feeding the Harlequin Shrimp thus becomes an easier task with no impact on wild Starfish populations.  Once the feeding situation is planned, all you need is a little bit of rock, possibly some macroalgae, and a good filter.  While shrimp do not require lots of space, they do demand excellent water quality.

Starting with these ideas, you can see endless opportunity for fun with "pico tanks".  Many of the Harlequins’ shrimpy cousins are also good choices as specimens for the tiny tank.  A single Coral-Banded Shrimp (Stenopus hispidus), Cleaner Shrimp (Lysmata amboiensis), or Blood Shrimp (Lysmata debelius) are all colorful and fascinating creatures.  Likewise, the freshwater Cherry Shrimp (Neocaridina) can be kept in small groups and will reward good husbandry with prolific reproduction.  Suitable fish can be more challenging to locate, but there are some excellent choices for both the marine and freshwater tank.  In addition to those mentioned above, some of the tiny Rasboras for freshwater and the miniature Basslets in saltwater work well in "pico tanks".   Be sure to research the needs of any invertebrates, fish, or plants to be certain that their care requirements can be met in the size of tank you’ve chosen.

To summarize, if you obey the cardinal rules of aquarium husbandry, you can easily and successfully maintain a "pico tank" in your own home. Plan carefully and assemble your system accordingly. Once you have established and populated your system, don't deviate from your plan. Adding "just one more fish" or invertebrate can spell disaster in a small volume of water. Discipline is mandatory! If you are up to the challenge, "pico tanks" can add an entirely new dimension to your hobby!