How many of you measure the temperature of the water when performing water changes?

Do you, do you not, why do you, why do you not?
I do not. Never have. Never had issues. I have heard of people killing their fish by not measuring the temperature. Have you?

For the Tilapia in the house, I do it by feel, and I can tell how close I am, by the temperature reading on the digital heaters ( I’ve gotten pretty good at matching )

On my regular tropical fish tanks, all make up water is room temperature RO water from my holding tank… I do typically add water just above the heaters, rather than on the opposite side of the tank

Same as Magnum, by feel. I run the hot tap from cold till the tote is half full then add cold. I usually get 20-23 on average. Plus I only do 10L WC's so temp cant be affected hugely since my tanks are 90L and 60L.

I always check. My water is first conditioned in a holding tank that has a thermometer. It is so easy to do and what the heck, prevents shocking the fish.

I have made mistakes, but generally after all this time, I can tell you the temperature by touch. If I have new fish, I'll make it maybe 2 degrees warmer than the tank, to not give Ich a chance to party. But generally, I have only had issues when the water was cold, usually if I try to do too many in winter when the water heater can't keep up the temp.

Here's a trick if you use a hose - aim an infra red temperature sensor at it from very close. It works.

I age my change water in a 40 gallon food safe plastic container under aeration . I also keep a 150 watt heater set to 82 degrees in it . When water change day rolls around everything I need is right handy where I need it all ready to go . 40 gallons gives me more than enough to do half in each aquarium I have .

@Back in the fold
Don't you love those Rubbermaid Brutes? I have a 32 and 4 of the 20s.

I pump most of the water both out of and into most of my tanks.

I need to check the temp. of changing water because I use 3 different temp. water for changes which depend on the tank temps and the what is going on int the tanks.. For my Hypancistrus breeding and grow tanks I set up water at 86F. It may be in the cans for a bit and I jusr need it to be about 82-86. By setting it up at 86 I know it can sit for a but and get cooler before it goes into tanks. But is should not drop below 82 before I use it.

However, if I have to do a dry/rainy simulation too try yo get the plecos intoan amorous state of mind, I need the end the dry season with the tank at 92F and then hit it twice within 36 or so hours with water in the low to mid 70s to drop the tank temps into the 78 -80 range. Then they are allowed to go back to a controller setting of 82f F.

Then there are my "cooler" water tanks in the 76 to 78F range. So, I generally set up changing water at about 77. Depending on the order I do them I let the few I have that want to be a bit below 77 get worked on last as the changing water will lose a degree or two before I get to them.

The biggest issue was my Altum tank in which I used an 11/9 mix of RO/DI and tap water. The RO/Di is stored at a temp. in the low 70s and the angel tank is at 85-86F. I need 20+ gals for a water change. I put the RO/DI into a 20 gal. can and then add hot water to it with a pump running to stir it. I check the temp as I go and when it hits 85-86 I fill any more space with 86F water.

Finally. I keep my clown loaches at about 80F in the 150 gal. I batch water for them at 86F as the amount of time I need to do all the maint. and then to drain 1/2+ of the water means that changing water will be close to 80Fot even a tad lower by the time it it goes in.

I have well water and I do not dechlor, but it contains excess CO2 which I am outgassing with my changing process as well as oxygenating the water. If I use just my cold it will be close to 55F coming out of the tap. But, in my pleco space in the other building I am able to refill tanks directly from the hose connected to the faucet at temp. But I normally put it into cans and pump it in. The ote water has a long run from the main house as out guest hose and storeroom do not have their own water heater. So getting hot water out there takes some time and wastes a lot of water down the sink. Filling the containers means I nay need to do two fills for all 8 tanks out there.

I turn on the hot water tap and while it is running, I put my finger in my tank and FEEL the approximate temperature. Then I FEEL the water coming out of the tap and adjust the hot and cold water taps as necessary to match the estimated temperature of the tank water. I generally am within 2 degrees of the original tank temperature as indicated on my tank's digital thermometer..

I use a Python Water Changer to drain and refill the tank.

I do it by feel. Give or take it's usually within 5 degrees difference.

After the amount of water changes I have done over the last year and a half I just do it by feel.

I have a dedicated thermometer for my tanks and for tap water. I am a stickler for making sure the tap water in an exchange is within two degrees or closer to the tank water.

Yea i learned the hard way about 8 years ago; killed my favorite pair of rams doing a water change during the winter and after that date i always pre-heat the new water to the tank before putting it in. Of course despite doing that then 2 years later we had a 20 hour power outage that killed my next pair of rams

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Of course these days i have backup generator Dwarf cichild are esp sensitive to large change in temperature and such will usually show up a few weeks later as bloat. Don't know about other fishes - my clown loaches seem to like a bit of water change now and then... but i wouldn't want to tempt fate. There are all sort of fishes out there from different type of waters and some are expose to large temp changes from time to time and some never see it.

I will say this about my that 2nd pair of rams; the minute the electricity was restored both rams swam next to the heater and stayed there till the water returned to normal temp. It was rather telling they did not like the cold.

These days my design is more sophisticated - for @TwoTankAmin it works like this:
hot water->
-> thermostatic valve (these are rather interesting devices with many different designs) -> charcoal block to remove chlorine -> tank
cold water->
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I was able to retire my brute buckets for holding water overnight to adjust temp btw the 40 gallon model is great for those with larger aquariums.
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If you ever want to reproduce this design you need to look into the different types of thermostatic valve as some are just not suitable for this sort of application - there are min/max on the hot and cold channels as well as high/low designs. Lots of different models with different parameters - find an eng from the company to explain the exact design of each valve they sell - it will help a lot

I do check temperature, but only by hand. I typically prefer the incomming water to be a bit cooler than the tank water for my sw tanks. Room temp new water into a slightly warmer tank can help stimulate certain coral activity as long as it's a smaller 10-20% WC and not something like 90% (then I'd want pretty similar temps). Back when I still had fw tanks, there was only one place I lived where I felt comfortable using the hot/cold tap balance method to match temp by feel. In other locations I lived, I didn't like to use the hot tap because the water from that contained more metals. In one particular complex, water out of the hot tap also tasted quite awful even if it was cooled down - not something you'd want to drink so not something I'd want in a tank. In those cases I just ran a bucket or two's worth out of the cold tap and either it was ok as-is (probably the only perk of living in a place where the cold tap was always a nasty luke warm lol) or I waited for it to come up to room temp. Where I currently live I have to wait by default; the water out of the tap can be as low as 40F / 4C which would easily shock a lot of animals if I pumped that straight into the tank. I even have to heat the output of my RODI for some time before I can even mix salt into it since nothing wants to dissolve at that temperature.

I use a mix of hot & cold tap water. By my finger test I can get to within 2 degrees or less of each tank unless I want it hotter or cooler for some reason. Likely to stimulate breeding or simulate seasonal changes. I only have 1 small heated tank these days so I pay more attention to that 1. But fish in the wild are used to cooler rains but buffered by larger moving bodies of water.

I have 2 tanks these days - a 9 gallon and a 6 gallon, I keep a 25 litre bottle of RO water in a cupboard with a little thermometer on the side, it's about 20°C depending on the time of year. I add 1 litre of boiled water to it before doing water changes and that brings it to about the right temperature for my changes. When I had a bigger tank it was harder but having these nano tanks has made life much easier I have to admit.