Rüdiger Rautenberg with an alternative look at aquarium heating and how following the ‘rules’ may be costing you money…

First I have to make clear that I will presuppose a few facts to keep this write-up at a bearable length.

The fish tank in question is situated in those parts of the world with a fairly moderate clime. That excludes on the cold extreme both pole caps, inner Siberia, parts of Greenland and basically all places, where ice and snow never melt. The other end of the stick would be the Iranian desert, Death Valley, the Fish River Canyon and maybe parts of Spain as examples of places with perhaps just a bit too much sun. Within the suitable regions said tank is located within a moderately well-built abode. The owner of the fish tank knows how to operate a thermometer and is willing to do so at reasonably regular intervals. When I talk about “additional heating” I mean any purpose-built aquarium heating devices such as, e.g., a heater stat.

Taking those basics into account, I will now argue that a vast number of commonly kept fish species can be maintained without any additional heating at all and further that the majority of commonly kept species can be maintained with limited additional heating only during about 3 (the coldest) months of the year.

In reverse I will argue that most fish species kept in our aquaria are kept too warm.

Er, did you dream that up dude?

Before I get to factual examples and practical considerations, I’d like to shed some light on how I came to question general temperature recommendations and my thoughts behind it.

How do we come to have all these wonderful temperature recommendations, which by the way as I’ll show later vary quite significantly for any given species depending on which source we have consulted.

Now, there is of course the climate data collected all over the world, even in the most inhospitable of all places. But temperature we get from those tend to be air temperatures not water temperatures.

Then, there are the people who collect fish. Not those who do it professionally mind you. They usually are poor peasants who can hardly afford the inevitable net and don’t bother with such profanities.

It’s scientists, out there to discover new species, ambitious and equally well off aquarists, there to collect certain species (of course often hoping to discover a new species too) and perhaps the odd unsuspecting tourist with the once in a lifetime chance to catch their very own Siamese Fighter or similar (and no clue that there could be new species to be discovered).

Let’s assume all of them dip the temp-stick into the puddle and actually somehow preserve the result. Surely that should give us a fairly accurate idea of how to set the temperature in our fish tank?

What if all temperature samples were taken within a fairly narrow time window of the year? General vacation time would be such a narrow window as would be travelling at times of bearable climatic conditions. And after all, many of the known collecting sites are not accessible for months on end, e.g., due to weather conditions, flooding etc.

What if the spot where the fish was caught isn’t where it usually dwells but rather the spot it ended up by hunting after prey or on it’s flight from a predator.

Unfortunately we just netted it before it could get back to where it would feel a lot more comfortable. I believe I don’t have to mention that temperatures in any given body of water are not uniform and differences by quite a margin are the norm.

If we look at an aerial photo of the Amazon basin for instance we will of course see the majestic river itself and a number of the larger tributaries. What we don’t see are innumerable medium sized and small tributaries, which are well hidden under a dense canopy of rainforest.

That in turn means, these rivers and streams don’t get any direct sun light, which would logically make them cooler compared to those those that do.

The fact that the majority of “aquarium sized” fish species are collected from these sheltered waterways doesn’t only influence temperature considerations but will also play its part in a later instalment of this series about lighting.

Concluding this prelude I’d like to introduce one example of fish species, which will demonstrate without a doubt that questioning the “facts” isn’t a bad thing at all.

Pseudomugil gertrudae, the spotted blue eye, a beautiful fish indeed.

I have taken temperature and pH recommendations from 3 different internet databases and one online shop, which of course will all remain anonymous:

db1. Temp. 24 – 28° C pH: 6.0 – 7.5

db2. Temp. 25 – 30° C pH: 5.5 – 8.5

db3. Temp. 23 – 30° C pH: 3.8 – 7.8

shop. Temp. 20 – 26° C pH: 6.5 – 7.5

At a closer look and a quick thought, these can only be parameters taken from different breeders with different approaches.

Temperatures and pH measured at the actual different collection sites as found here show something quite different.

Temp. 12 – 34° C pH: 3.68 – 9.4

Database 3 is closest with the widest pH spectrum whereas the shop sort of convinces by allowing for lower temperatures. The fact is however that P. gertrudae certainly is a species that could be kept and maintained long-term without additional heating in most scenarios, as shown by actual and factual parameters.

So you want me to dump that heater?

Not at all. It’s always good to have a spare piece of equipment collecting dust somewhere.

But seriously, let’s see what it looks like at my place. I currently run 7 fish tanks of various sizes. But I only have 2 heaters, 100 and 50 watts, on temporary duty in my 160 l South American set up and my 54 l Dwarf Puffer tank respectively.

Temporary means they get switched on beginning of November and switched off end of January, latest mid February if winter is really long.

Now, does that mean my fishes get cold? I haven’t seen them getting their socks out so far. And there’s no need for that either. The S.A. tank sits in the dining room, which is obviously heated to a habitable temperature of about 20° C.

All other tanks are in my study come home office. Here too temperatures are kept at a bearable level, which in my case is a snug 19° C during the day. In addition, both “heated” tanks have closed light fittings, 21 watts T5 for the large one and a modified 16 watts (2x8w) CFL for the smaller.

At an ambient temperature of 19° C those lights raise the water temperatures by 3 and 4° C respectively. You will see that the heaters don’t have to work too hard to get the water to the desired 24 ° C.

In those periods leading up to switching the heaters on and from switching off to really warm weather, water temperatures can go down to 21 and briefly even to 19° C. None of my fished has ever shown any damage or discomfort due to low temperatures, quite the opposite, they are vigorous and strong specimens indeed.

I believe that generally recommended temps are actually breeding temps and as such not ideal for general, long term maintenance. If our fishes are constantly in breeding condition, triggered by the warm water, they are constantly suffering a huge amount of stress.

Putting on their “Sunday best”, courting, defending a territory, the actual spawning and, in some cases, caring for the brood and that over and over again take a lot out of the males. But the females too burn out quickly due to continuous harassment by the males and constant egg production.

My experience shows that keeping my fishes well below the recommended temperature for most of the year only has advantages. They are lively and active, look strong and show great colours, and they seem to get to a much higher life expectancy.

But then again, cooler water slows down the metabolism as we all know and that in turn prolongs the lifespan.

When temperatures rise up to and sometimes above their ideal breeding temps, they look after the fun side of business too and except for my Otocinclus spp. and those fishes I acquired only recently, every species I am presently keeping have spawned in their regular set up.

Badis badis regularly spawn and successfully raise young at 19° C, all Danio spp. spawn continuously at the same temperature so that I actually cool them down to 16° C for three months at least, Crossocheilus reticulatus are courting at 19° C unfortunately without subsequent spawning activities so far.

One of my Pangio semicincta females has gotten curiously full around the hips an I only had that group for about 4 weeks now. Doesn’t that somehow indicate, “Not too bad old chap”?

And let me add one bit of info that I unfortunately cannot conclusively tie to lower water temperatures but I also cannot see it as a coincidence that, as a matter of fact, I did never, since I am proceeding as described, have had any fish disease in any of my tanks, none whatsoever.

What’s that you mumbled about saving money?

Right, if I heated all my tanks to the generally recommended temperatures I’d have a bill just for the aquarium heaters of roughly € 680,- per annum whereas my actual bill for the same purpose is less than € 30,- per annum. That is a lot of fishes to buy!!

Was that it?

To finish this up I’d like to say, as someone who has lived and spent some time in the tropics, that even there things are not as constant and always level as they are made out to be.

There are more factors influencing water temperature for instance than just continuous sunshine. Or as an old friend of mine would say: “It ain’ warm where the sun cain’ git.”

What else happens “where the sun cain’ git” I’ll tell you about in the next episode.