My 24-litre Windowsill Tank

This aquarium was set up as nothing more than a place to dump unwanted plants and surplus shrimps. As it turned out, it became an interesting project in its own right.

Hardware

As with all my planted tanks, the substrate is very simple: a 50/50 mix of pond soil and silica sand topped with a layer of silica sand of similar depth. This provides a good rich substrate for the plants, while also giving the livestock something they can root about in.

There are no lights on this tank. The plants get all the light they need from the Sun, in this case by positioning the tank on a bright, east-facing window. The tank gets direct sunlight for only part of the day, more in summer, less in winter, but overall it seems to work very well.

Filtration was initially handled by an air-powered box filter. This has since been replaced with a small Eheim ‘Aquaball’ filter. During winter a heater is used to keep the tank from getting too cold, but during the summer the heater is removed. Even without the heater, summer temperatures cycle between about 18 degrees C at night and 30 degrees C during the day. While this sounds extreme, the animals and plants don’t seem to object.

Water chemistry

This tank was initally set up as a plain freshwater tank. This worked very well, but with the switch to keeping desert gobies, the tank is now slightly brackish, running at about SG 1.003. The shrimps, snails and plants do not seem to mind.

Plants

Various plants have been grown in this aquarium. Hygrophila cormybosa and Hygrophila polysperma did very well, to the extent that their stems go to more than 60 cm above the waterline and produced numerous purple flowers. The downside was that their roots became so robust and tangled that the aquarium now had very little swimming space!

The tank is now mostly stocked with Cryptocoryne wendtii, a few Vallisneria plants, Java fern, floating Indian fern, and some floating Salvinia. Regular pruning is essential, and in the case of the two floating plants needs to be carried out on a weekly basis. In part, the rampant growth of these plants has surely helped ensure good water conditions despite the small size of the tank.

Fish

Numerous different fish have been added to this tank, particularly juvenile catfish, livebearers and halfbeaks. At the moment the tank contains a trio of ‘golden’ Desert Gobies, Chlamydogobius eremius.

Invertebrates

Freshwater invertebrates do exceedingly well in this aquarium, benefitting from the ample supply of algae and organic detritus. Besides the various snails that came in with the plants, juvenile Yellow Helmet Snails, Tylomelania sp., are added to the tank on a regular basis. The adults are in another tank, but because of the Assassin Snails, Clea helena, in that tank, the juvenile Tylomelania usually end up being eaten if left with their parents. In the windowsill tank they grow rapidly.

Cherry Shrimps, Neocaridina heteropoda, happily breed and grow in the aquarium. To some degree the gobies view the juveniles as food, but secure places like the inside of the filter usually contain lots of shrimps of all ages.

Maintenance

A tank this small requires quite a bit of care in some ways, particularly with regard to the plants which tend to take over the tank if not pruned back. The filter also becomes clogged very quickly, and so needs to be rinsed every week or two. On the other hand, water changes aren’t particularly difficult to do, being limited to one 10-litre bucket every week or so. Evaporation can be a problem, and the tank needs to be topped up every few days during the summer.

Green algae is a particular issue worth nothing; the strong, direct sunlight this tank promotes the growth of this type of algae, and over time it clogs up the filter and smothers the plants. It isn’t difficult to remove by hand though.

Overall, this is a low-maintenance tank, and a surprisingly entertaining project suitable for any aquarist with a sunny windowsill upon which a small tank might be placed.

Various cuttings were added to the tank including two Hygrophila species.

A few weeks later and the Hygrophila have grown far above the waterline.

Desert gobies (Chlamydogobius eremius) thrive in the slightly brackish water conditions, and are completely indifferent to the high summer temperatures, as you would expect given their natural habitat. Here, a male guards eggs laid on a plastic plant pot.

Positioning the internal filter sideways makes it easier to fit inside this small tank. Shrimps and snails spend much time on the outside of the filter, pecking away at organic detritus.