I’ve been doing research recently into fish that have their minimum temperature at around 20 degrees. There has been articles in the past on here and in other places ( this is one of my favourites:
https://www.practicalfishkeeping.co.uk/features/how-to-set-up-a-temperate-tank-that-looks-tropical/ ) on setting up temperate tanks, but they are often focussed on fish that can tolerate temperatures like 16-18 degrees Celsius and so are fine in an indoor unheated tank in a heated home. It struck me though that oftentimes having a heater is still recommended in these instances as a just in case measure e.g. you go away for a weekend and the house cools down. It is also apparent that some of these species would struggle to deal with warm summer room temperatures with chillers and/or air stones often being recommended in the hottest months to ensure the fish don’t overheat. This really defeats the object of trying to go for a temperate tank in my view as there is significant added complication here.
So I got to researching fish with a minimum temperature of around 20 degrees. A heater could be used in the tank to prevent the water dropping below this minimum temperature but the summer temperature issue goes away because the fish can cope with higher temperatures. The other advantage is that this strategy would potentially allow the stocking of hillstream loach (given some flow top of course) alongside other fish - a species that I’ve had my eye on for ages! Also whilst the article I’ve linked suggests no problems with plants at cooler temperatures this does not match with my experience with some of the less hardy plants than those the author chooses. In summary I’m shooting for the middle ground compromise position - one I assumed wouldn’t really be possible... but I was pleasantly surprised!!...
Below is my current list of fish species that I would ordinarily consider a full tropical species which my research (mainly using Seriously Fish) indicates would work at this middle ground 20 degrees temperature (and above). I is certainly not exhaustive as I’ve *mainly* stuck to South American fish and I like the smaller species so won’t have researched fish that don’t tickle my fancy... but if anyone want to add to it I can edit this post. Some of my thoughts for where I might potentially transition my stocking towards are also shown. Interestingly many of the species I already own could be part of such a tank too.
Schoolers:
Neon/ Green Neon Tetra 21
Lemon Tetra 20
Red Phantom Tetra 20
Black Widow Tetra 20
Red/Black Phantom Tetra 20
Flame Tetra 20Bottom Feeders:
Hastatus/Habrosus Cory 20
2cm Nanos:
Ember Tetra 20 - I have these already
Celestial Pearl Danio 20Feature fish:
Apistogramma Borelli 20
Dwarf flag cichlid 20
Fiveband Barb 21Top dwellers:
Dwarf Pencilfish 22 - I have these already
Golden Pencilfish 21
Marbled Hatchetfish 20
Rocket Killifish 20
‘Surface’ dwellers:
Otocinclus 21 - I have these already
Hillstream Loach 20