Lowest water temperature tropical fish can survive

[Chris93]

Hi all

Just have returned from the holidays yesterday, to find out that absolute disaster happened to my fish tank.

To shortly introduce to my fish tank, it’s just a generic 70l. Which I filled with the fine sand from b&q and fluval plant substrate, then added some rocks and driftwood. Planted with about six different plants (im not good at remembering their names) and bunch of Java moss.

As a water parameters are super stable, for about a year I would change water once every couple of weeks, when I felt like substrate could do with some cleaning. I don’t change filter cartridges at all, just flush them with used water.

Unfortunately, after arriving back home after eight days, I found out that electrics went off and central heating switched off as well.

I rushed to the tank to find out that six neon tetras, two guppies, a bristlenose pleco and one molly sadly died.
However, two mollies and three amano shrimps survived.

Water temperature was only 9 degree Celsius and looks like heating went off at least four days ago, when temperature outside was even lower.

I tested the water and despite some of fishes starting to decompose quite a bit, only nitrates risen slightly, but still below 50mg/l. Oxygen levels must stayed fine too, as none of survivors were gasping. Maybe low temperature slowed ammonia growth down?

This sad event left me with question I struggle to find answers to.
What’s the lowest water temperature tropical fish can survive for several days? I can only find advices regarding recommended temperature.
Why molly and amano shrimp seems to be more robust, when recommended temperatures for them are similar to other species?

[Martinspuddle]

What’s the lowest water temperature tropical fish can survive for several days? I can only find advices regarding recommended temperature.
Why molly and amano shrimp seems to be more robust, when recommended temperatures for them are similar to other species?

Greetings & welcome to

Sorry to hear of your loses.

Not many tropical fish species can survive low temperatures.

Poecilia sphenops can tolerate some lower temperatures, 16°C but 9°C is very low and I'm quite frankly surprised they have. Amano shrimp can survive in a temperature of 18°C but I should imagine not for very long any lower.

Think you've been lucky, just make sure you gradually raise the water temperature so not to shock the remaining fish and shrimp.

I tested the water and despite some of fishes starting to decompose quite a bit, only nitrates risen slightly, but still below 50mg/l. Oxygen levels must stayed fine too, as none of survivors were gasping. Maybe low temperature slowed ammonia growth down?

Ammonia and nitrite oxidation are strongly influenced by temperature but to what levels I'm not entirety sure. @black ghost or @Vale! probably have a better understanding of that subject.

[Bluetaurus]

Hi and welcome.
Sorry to hear about the loss of fish.

[plankton]

Welcome to the forum.
Sorry to hear of this.
As Martin says they are unlikely to survive long in low temperatures. Some fish will last longer than others, depending on genes and metabolisms.
Cooler water holds oxygen better than warmer so that's why that was ok. I don't know what happens with ammonia, but I shouldn't think it makes a lot of difference. If the corpses were rotting then there would have been enough generated to be toxic. The "munchers" in the filter would have gone dormant so that certainly wouldn't help.
I have found that it takes a while, probably even a day or so, even in smaller tanks, for the water to dissipate heat, especially with a lid on the tank.
Did you have someone feeding them while you were away?

[Chris93]

Thanks all for replying

I have a lid on this tank, but the water still dropped to the temperature of the air indoors.
As I left only for a week, didn’t ask anyone to feed them.

[plankton]

I was a bit worried that if someone had been feeding them they'd made a mistake which would have compounded the problem, that's the reason I asked.