The 20 Degrees Club

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 20

Bottom Feeders:
Hastatus/Habrosus Cory 20

2cm Nanos:
Ember Tetra 20 - I have these already
Celestial Pearl Danio 20

Feature fish:
Apistogramma Borelli 20
Dwarf flag cichlid 20
Fiveband Barb 21

Top 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

Are you just researching or are you considering setting up a temperate tank? 

@Sue you raise. Good point here - do you think that having the tank temperature at the fishes minimum for the winter months is too long? Many of these species will be use to seasonal fluctuations would they not?

My gut feeling is that it is OK to be at the lower or higher edge of the temperature range for short periods such as a cold snap in winter and a heatwave in summer.

But I am aware that this in the reaction of someone who lives in the British climate which is prone to short lived swings to the extremes. In other countries at our latitude, it is hot all summer and cold all winter with a transition period between. (I once had a Polish neighbour who said that in Poland, it got colder through autumn, stayed cold all winter then got warmer in spring. She blamed our fluctuating climate for things like the common cold) In the tropics the temperature varies diurnally rather than seasonally.

I don't know what the climate is like in those areas where the temperate fish in the hobby originate. Are they like Britain which has short lived hot and cold snaps, and the fish survive those low temperatures for a short time but could not cope for months? Or is the climate in their places of origin more akin to central Europe, where it gets cold and stays cold till spring?

I find myself coming back to this topic given the rising costs of electricity…

I also have a realisation from my previous work in that I was previously attempting to find tropical species that could go as low as 20 degrees, rather than exploring temperate species too. Whilst I would want to accommodate some of my existing fish if I was ever to go for a lower temperature tank, there is no need for me to restrict myself to adding only ‘tropicals that will manage that low’.

Anyway long story short, I’ve kind of settled on the below as a potential stocking plan

Schoolers:
Flame Tetra 20
Zebra Danio 18
Ruby Barb  18
Ember Tetra 20 - I have these already

Bottom Feeders:
Julli Cory 20 - I have these already

Feature fish:
Dwarf flag cichlid 20

‘Surface’ dwellers:
Hillstream Loach 18

Nerite snail and Amano shrimp - I have these already

All this really means for now is that I can replenish my aging population of ember tetra. When my existing schoolers (cardinals and rummynoses) pass on Flame Tetra or Zebra Danio would be the logical replacement species. I may also look into getting the dwarf flag cichlid now as I found myself wanting to get dwarf cichlids again just recently.

This is one of those many reasons this forum is great… you are all able to look at my excited scribbles from a more sensible standpoint and bring me back to reality!  Quite right… if I want to go to say 20 degrees I need fish that go lower than this. I think I was assuming in summer the tank would go hotter and there would be a seasonal fluctuation. But I guess the ‘winter’ at 20 degrees would be too long. What I would want to avoid is having to cool the tank in summer so I will turn my research to that now… I suspect there is no perfect answer here…