Mine are in a fairly wide 4ft, (which is around 56 g -US) the smallest I think I would go for heat transfer and water quality would be 3 ft at a pinch 2 ft. Its not that they are a huge fish as you can see incomparison to my peppered corys, nor are they super active zipping all over the tank like crazy danios. Its just the need for good cool water, and a larger tank allows for better temp stability. The only site I can find that suggests a tank size for these guys is a 20g tank, while another site suggests a 12 g(US) tank. And after a few more searches another places reckons a min of 10g. But then most of these are also saying to keep them in smaller groups of 1 male 2 female. Where as I have at last count around 13 (maybe one or two more, I have a habit of getting any loners in shops if I find them- they are a social fish)
Even though these guys are meant to only like cooler water mine have sailed through some shocking summer heats and done equally well in the depths of winter when their tank can get down as low as 18 degrees cel. The heat mine have survived is not ideal and probably pushing their limit of endurance but the 18 degrees cel is still within a safe range for them, just.
Also mine like being contrary to all the information and regarding plants, they love hiding in them, cleaning the leaves of them and generally just resting on them. They do have stones as well and even a large flat slab of stone that is angled under the inflow from the HOB filter. This is generally the first feeding station that any new Borneo's learn to eat at before they discover all the other places in the tank. I can't say mine have shown huge interest in things like defrosted bloodworms but they do like tropical tetra min flakes, tetramin greens flakes, and Hikari catfish wafers, as well as my crayfish pellets that are for my shrimp. They are not interested in fruit or veg like Pleco's and never damage my plants. Some nice green algea covered rocks are also a great food source for these guys. And of course they do an amazing job on glass.
Oh and to top off them being pretty, peaceful and generally cute they also wink at you like corys will
, nothing beats a winking fish
.