When most people think of an unheated, so called cold water, tank, they will often think that you keep goldfish. This can be the case but is not always true, and if you are considering keeping fish, but would prefer to save energy by not heating a tank, there are more options.
First thing’s first, a tank kept at room temperature is NOT a cold-water tank. At 18-20°C a tank is considered to be temperate and true cold-water species (which are hard to come by) are not suitable. Goldfish can be kept at these temperatures but when you consider they can grow to 35cm (that’s 14”) they are not suitable to most aquariums. Fancy goldfish are smaller but have a lot of in bred issues, causing, amongst other things, swim bladder issues and are prone to tearing their fins on tank décor. So as most of us want happy, healthy fish, ands don’t have a 4 foot plus aquarium, perhaps we should look at other options.
The best size tank to consider as a starting place would be around 60cm (2’), they don’t cost much more than the smaller options and it is much easier to get the water quality right in a larger tank (and you can clean it less often!). This size gives you the option of having several small groups of different species, giving lots of interest in the tank.
Some good fish to start with would be White Cloud Mountain Minnows (Tanichthys albonubes), and Zebra or Leopard Danios (Brachydanio rerio) both very hardy fish which like to shoal in groups of six or more. Both are very active so will benefit from plenty of open swimming space in the aquarium and provide hours of entertainment.
If you’ve gone for a nice sized tank you should still be left with plenty of room to add some more colour to your tank with the addition of some Barbs. Rosy Barbs (Puntius conchonius), Golden Barbs (Puntius semifasciolatus), and Odessa Barbs (Puntius ticto) are all good options and will develop distinctive, colourful markings as they grow. Best kept in groups, they only grow to a few inches so keeping a mixed group will give colour and interest as they display to each other.
Paradise Fish (Macropodus opercularis) are slightly larger (around 4”) and have beautiful long fins. Males will fight so keep them in groups of one male with several females. They need a lot of swimming space and plenty of hiding spots to avoid them getting stressed. It is also best not to keep them with Barbs as they can be a bit too boisterous for them or nip at their long fins.
If you are feeling a little more confident, and don’t have any long-finned varieties, you can go for Buenos Aires Tetra (Hemigrammus caudovittatus) and the Bloodfin (Aphyocharax anisitsi). Again, best kept in groups, they are both fairly peaceful, but can be nippy so best make sure there is plenty of room for other species to retreat, just in case.
Finally, no tank is complete without a cleaning crew! Corydoras are great for this, scavenging left over food, eating algae build up and adding interest to the lower part of the tank. Available in Peppered, Bronze and Albino varieties, they like to live in groups and are great additions to the tank. Just be sure the substrate (gravel, sand etc) is free from sharp pieces and drop in some sinking pellets or frozen/live foods to complement their scavenging.
So, your tank can be just as interesting as a heated tropical tank and you don’t have to (and probably shouldn’t) have goldfish!