What temperature difference will shock a fish?

[Karen B.]

Greetings!
 

When I do WC, I always use a thermometer to try and match the temperature of the tank as closely as possible. Still, I was wondering what is considered a « safe » zone? 1f of difference? 2? 5? 
 

Thank you

[scott the fishman]

On 2/26/2022 at 1:30 PM, Karen B. said:

Greetings!
 

When I do WC, I always use a thermometer to try and match the temperature of the tank as closely as possible. Still, I was wondering what is considered a « safe » zone? 1f of difference? 2? 5? 
 

Thank you

Iwas like you and use a thermometer and buckets. to make sure the new water was the same temp. after wat5ch8ing coop vids primetime aquarium vids on WC learned to just us my hand as a temp indicator i never had a issue and i am always right there around 1-2 degrees. for how many degrees can the water change in a very small amount of time i have heard a few opinions i always stay between1-3degrees of water temp difference. hope that helps. heres a trick that works well with end of the hose submerged in the tank i put my fingers in from of the water flow from the hose if i feel a temp difference i adjust to it. i am usually spot on.

[YeePuffer]

I’ve always have been just going by feel and haven’t had an issue. Also refilling the tank with slightly cooler water can trigger spawning in a lot of species. 

[lefty o]

slightly warmer isnt a problem, but much colder will stress them. i try to keep it within approximately 5 degree's.

[Widgets]

Have you ever gone into a swimming pool in the summer where the first few inches of water were much warmer than the water below?

Have you ever seen a fish in the wild surge from the depths to catch an insect that has fallen onto the surface, then go back to the depths?

We tend to be overly protective of our finned friends. It is usually a good thing, as our small ecosystems that we keep already provide more stresses than they get in the wild. Just like in people, too much stress can leave them more vulnerable to illness.

I just go by feel. If there is not a big difference in the temperature, and you are adding the new water at a reasonable rate (to not disturb the decor), and you have some flow in the tank; I would expect the temperature to equalize fairly quick.

My fish like to play in current from power heads and the HOB outflow. They gather at the flow from the water changes too. If it was stressing them, I would expect them to avoid it.

[Colu]

I use a temperature probe to get between 0.5-1 degree that way I don't stress my fish out

[Wrencher_Scott]

Ya, it's not that critical. Like @Widgets said, they swim in differing temps all the time.

Look up thermoclines. 

[Odd Duck]

I think it depends on the species and likely also somewhat on the individual.  It probably doesn’t usually matter much as long as you’re within a few degrees, but in the wild, it’s the fishes choice.  We don’t give them a choice and if they start having issues, they have nowhere to go.  If they have issues they’re hiding, then a big temp change could be much more of an issue.  I typically try to keep it within 5 degrees or less and usually it’s within a couple degrees.

I sometimes deliberately WC with cooler water to trigger spawning (5 or so degrees cooler for a 25% WC means at most only a couple degrees change for the tank. With my adult Jack Dempseys who I do NOT want to breed, I make sure their WC is at least equal to, or slightly warmer than, tank temp.

[modified lung]

Sudden change of 5°F for larval/juvenile and 20°F for adult fish can almost immediately kill.

Sudden change of 9–15°F in adults can cause digestive issues, abdominal swelling, stress disease. Sudden increase of the same amount can cause ammonia to accumulate in the fish's blood. These can kill after a short time.

And there's always differences between species.

[Cinnebuns]

Disclaimer:  no fish were harmed in the making of this experiment

I've recently thought about this and even did an experiment. What got me thinking about it is the fact that doing "cold" water changes will trigger cories to spawn. Btw "cold" more means coldER. It's not like I'm putting 50 degree water in. Anyway, I thought about it because I also have guppies in the tank. I didn't want to shock them. 

Using a thermometer, I added water 5 degrees colder than the tank temp. I then tested the water temp immediately and after 30 min with the heater off. The temp only changed by 1 degree. I then tried it another day with 10 degree temp cooler water. The temp only changed by 2-3 degrees. That's still not much of a change and I saw no stress reaction from the fish. 

The point is, if you are doing a 20-30% water change, not getting the exact temp of the water isn't going to make much of a difference after that new water mixes with the temp already in the tank. If you get it close, but not quite on, I'm sure the fish won't even notice let alone get shocked. Now, I wouldn't say you should do 10 degrees cooler, but if you are off by 1-3 degrees I don't think it will make a difference. 

Edited February 27, 2022 by Cinnebuns

[StanF]

On 2/27/2022 at 2:10 AM, Cinnebuns said:

Disclaimer:  no fish were harmed in the making of this experiment

I've recently thought about this and even did an experiment. What got me thinking about it is the fact that doing "cold" water changes will trigger cories to spawn. Btw "cold" more means coldER. It's not like I'm putting 50 degree water in. Anyway, I thought about it because I also have guppies in the tank. I didn't want to shock them. 

Using a thermometer, I added water 5 degrees colder than the tank temp. I then tested the water temp immediately and after 30 min with the heater off. The temp only changed by 1 degree. I then tried it another day with 10 degree temp cooler water. The temp only changed by 2-3 degrees. That's still not much of a change and I saw no stress reaction from the fish. 

The point is, if you are doing a 20-30% water change, not getting the exact temp of the water isn't going to make much of a difference after that new water mixes with the temp already in the tank. If you get it close, but not quite on, I'm sure the fish won't even notice let alone get shocked. Now, I wouldn't say you should do 10 degrees cooler, but if you are off by 1-3 degrees I don't think it will make a difference. 

This right here.  I saw a video a while back by a fishtuber called Ben O'Ciclid (I think...) where he did this exact experiment and showed how the tank temperature doesn't change much when you do a water change. He had some larger sized tanks so I expect that the bigger volume of water helped to moderate the temperature swings, but the principle here is correct.

As long as you get the water "close enough" by feel, you won't really affect the temp in your tank.  Keep in mind,  this doesn't apply if you do large water changes in a small tank.

StanF

[Flumpweesel]

I only worry about temp if I'm doing a change bigger than 50% I've done water changes around the 20% mark and not even seen the heater click on.

My tanks are only around 25C though so the temp gradient from tap to tank is probably not that huge. And I add the water slowly over about an hour. Most of the fish come over and play in the flow for a bit.

[lefty o]

On 2/27/2022 at 1:10 AM, Cinnebuns said:

Disclaimer:  no fish were harmed in the making of this experiment

I've recently thought about this and even did an experiment. What got me thinking about it is the fact that doing "cold" water changes will trigger cories to spawn. Btw "cold" more means coldER. It's not like I'm putting 50 degree water in. Anyway, I thought about it because I also have guppies in the tank. I didn't want to shock them. 

Using a thermometer, I added water 5 degrees colder than the tank temp. I then tested the water temp immediately and after 30 min with the heater off. The temp only changed by 1 degree. I then tried it another day with 10 degree temp cooler water. The temp only changed by 2-3 degrees. That's still not much of a change and I saw no stress reaction from the fish. 

The point is, if you are doing a 20-30% water change, not getting the exact temp of the water isn't going to make much of a difference after that new water mixes with the temp already in the tank. If you get it close, but not quite on, I'm sure the fish won't even notice let alone get shocked. Now, I wouldn't say you should do 10 degrees cooler, but if you are off by 1-3 degrees I don't think it will make a difference. 

exactly. if you are fairly close, the actual temp change in the tank is a fraction of the difference of the temp of the water you are adding. for the standard 20-30% water change, if you are close, you are fine.

[Torrey]

On 2/26/2022 at 2:30 PM, Karen B. said:

Greetings!
 

When I do WC, I always use a thermometer to try and match the temperature of the tank as closely as possible. Still, I was wondering what is considered a « safe » zone? 1f of difference? 2? 5? 
 

Thank you

It depends on the type of livestock, and the goal of the water change.

Many fish require a cooler water change to simulate the rainy season and spawning conditions. Some shrimp require water changes to include a drip acclimation.

Most aquatic animals don't die when a downpour drops the water temperature by a few degrees, and my larger tanks have traditionally offered a couple of different "temperature zones" as fish are generally wiser than we are regarding meeting their needs.

Some fish (I'm looking at you bettas & discus) are more likely to develop opportunistic infections with rapid temperature drops.

Meanwhile, many cories are more likely to spawn🤷‍♂️

Watch your fish. Color changes, flashing, and rapid gill movements (increased respiration) are indicative of stress. Either add the water more slowly, or identify what is distressing the fish and alleviate the issue.

[tolstoy21]

Yeah, I would agree that moderate differences in temp don't matter tremendously. I've even become pretty brazen with my crystal red shrimp these days to, as I will move them from one tank to the next, or do a water change, and as long as I'm not like 10F off in temps, I just don't worry about it anymore. I'll do a 30% water change on them with water that maybe 5F off and the temps stay pretty solid.

I tend to treat Ph the same as long as I'm within 0.5 degrees or so. But this can be species dependent, as I killed a bag full of L397 pelcos by moving them from one Ph to another too quickly--death by plop-and-drop! 😞  Worst day ever!

On second thought, given the above, maybe it's safer to ignore everything i just said!   😛

Edited February 28, 2022 by tolstoy21

[tolstoy21]

On 2/27/2022 at 2:10 AM, Cinnebuns said:

It's not like I'm putting 50 degree water in.

I use a drip system for many of my tanks. This changes anywhere from 2-4 gallons an hour on 20 highs (and a few 40 breeders) 2x daily. I guess I probably change 25% - 40% volume daily, depending on the tank.

The fresh water going in is about 50-55F in the winter, a tad warmer in the summer.

Water goes in slowly, spaced over many short intervals. 

Over all, the temps will only fluctuate 3-5F during the course of the day. I've been doing this a few years now and have not seen any adverse effects on any fish species I keep. I keep all my tanks at between 74F and 82F.

Edited February 28, 2022 by tolstoy21

[Andy's Fish Den]

It would all depend upon how much water volume is being changed, temp of water in tank and the water being added. I purposely will use cold water to trigger fish to spawn, especially corydoras species, I have drained 40-50% of the water from a 20 gallon, and added in water that was 15* cooler and not had any issues, it actually only lowered the tank temp by about 5 degrees when it was filled. Now, you also have to consider, I didn't just dump the water in either I had it trickling in over a period of about an hour trying to simulate rainfall. 

When I am doing my regular water changes, I just do it by feel, and get it close, and maybe just slightly cooler rather than warmer.

[AndEEss]

I put a suction-cup thermometer on each end of my 75g when I do water changes and keep my powerhead going. The circulation helps get uniform dispersion and I'm able to watch the temperature for any variations when I'm changing the water. 

Maybe I'm weird, but I pull water out via a siphon at the same time as I'm putting it in via a Python from my sink.  I add Prime before and during the water change. My siphon is basically a 2' piece of PVC with an end cap, drilled with a bunch of 1/8" holes just above the end cap, with a ball valve on it at the top, and 5/8" vinyl tubing which heads out my front door and down to my lawn. Fish can't sucked in or stuck to it, but poop can be sucked in just fine. The end cap keeps it from going into the sand or sucking any of it up.

[Torrey]

On 2/28/2022 at 9:14 AM, AndEEss said:

I put a suction-cup thermometer on each end of my 75g when I do water changes and keep my powerhead going. The circulation helps get uniform dispersion and I'm able to watch the temperature for any variations when I'm changing the water. 

Maybe I'm weird, but I pull water out via a siphon at the same time as I'm putting it in via a Python from my sink.  I add Prime before and during the water change. My siphon is basically a 2' piece of PVC with an end cap, drilled with a bunch of 1/8" holes just above the end cap, with a ball valve on it at the top, and 5/8" vinyl tubing which heads out my front door and down to my lawn. Fish can't sucked in or stuck to it, but poop can be sucked in just fine. The end cap keeps it from going into the sand or sucking any of it up.

It would be wonderful if you were to make a how to video build for this🤞

[AndEEss]

I'll take a picture of it when I get home. 

[Patrick_G]

On 2/28/2022 at 8:14 AM, AndEEss said:

Maybe I'm weird, but I pull water out via a siphon at the same time as I'm putting it in via a Python from my sink. 

What method do you use to measure how much water you’re removing? 

[AndEEss]

On 2/28/2022 at 10:04 AM, Patrick_G said:

What method do you use to measure how much water you’re removing? 

I put a 5 gallon bucket at the bottom of the hose that is draining and time it to see how long it takes to fill. From experience, that's generally about 2min. I have a Sharpie mark on the ball valve to maintain the correct position and flow rate. So, if I'm doing a 50% water change, assuming I have roughly 60 gallons in the tank after hardscape, substrate and a slight gap at the top, I drain and fill for 12 minutes. 12 minutes at 2.5gpm = 30 gallons.

I also do a NO3 test at the start and end; my results are generally consistent with chopping my nitrates in half (20==>10ppm).

Edited February 28, 2022 by AndEEss

[Wrencher_Scott]

I worry MUCH more about chlorine in my tap than temp. With that being said I do get it pretty close to the tank temp but like I said I don't think it is all that big of a deal.

[Torrey]

On 2/28/2022 at 9:39 PM, Wrencher_Scott said:

I worry MUCH more about chlorine in my tap than temp. With that being said I do get it pretty close to the tank temp but like I said I don't think it is all that big of a deal.

Chlorine is easy to deal with, just add Prime. I finally have a TDS meter.... It's one thing to make jokes about liquid rock coming out of the tap... totally different to see the hard numbers and know I have slowly been killing plants with too much calcium.

(Not trying to make light of your concern over chlorine... more of trying to acknowledge we all want to do best for our fish and plants... and overcoming challenges is a learning opportunity in the hobby)