Sudden fish death after water change! help!

[Lexi B]

Hello all. I have a bit of a problem. Today I did about a 20-30% water change on my five gallon tank with 4 guppies and 4 pygmy corydoras in it. It's a temporary set up for a 20 gallon long. 

Before the water change, all of my fish were very happy and active as always. 

Within five minutes of the water change the guppies have started swimming extremely slowly, but the cories were in bothered. I don't know what exactly happened, but about an hour has passed. 

The guppies are still huddled in the corner of the tank and hardly moving and I found one of my poor baby cories dead!

I don't know what I did wrong. 

The tank is about 3 months old, fully cycled. 

It has 0 ammonia, 0 nitrite, and typically 5 nitrate. The temperature stays at around 78 degrees. The pH is a solid 7.

I'm new to the hobby and I don't know what on earth I did wrong. The tank gets weekly water changes. 

My only thought is something went wrong with the tap water or the bucket I used.

(which was only ever meant for fish water)

[Fish Folk]

So sorry to hear... it’s sad when we lose fish in the hobby. No ideas for sure, but here’s a couple possibilities:

(1) Was the temperature of the water you added close to that of the tank? If not, it can shock fish.

(2) Did you remember to add dechlorinator? Sometimes it’s easy to get distracted and forget. Chlorine or chloramine really can bother fish.

(3) Have you done a water test on your _tap_ water? Sometimes ours has a spike in ammonia, which can kill off sensitive fish. We use Fritz Complete water treatment, which (claims to) chemically bind ammonia, nitrite, and nitrate along with treating tap water for chlorine & chloramine. 
 

(4) Sometimes a water change with tap water that hasn’t “gassed off” (rested) will give fish something like the bends — what divers get — loads of tiny bubbles unsettle them. 
 

There are downsides to working with small tanks. Parameters can just go out of control much faster than when there’s a larger volume of water. 

[Lexi B]

2 hours ago, Fish Folk said:

So sorry to hear... it’s sad when we lose fish in the hobby. No ideas for sure, but here’s a couple possibilities:

(1) Was the temperature of the water you added close to that of the tank? If not, it can shock fish.

(2) Did you remember to add dechlorinator? Sometimes it’s easy to get distracted and forget. Chlorine or chloramine really can bother fish.

(3) Have you done a water test on your _tap_ water? Sometimes ours has a spike in ammonia, which can kill off sensitive fish. We use Fritz Complete water treatment, which (claims to) chemically bind ammonia, nitrite, and nitrate along with treating tap water for chlorine & chloramine. 
 

(4) Sometimes a water change with tap water that hasn’t “gassed off” (rested) will give fish something like the bends — what divers get — loads of tiny bubbles unsettle them. 
 

There are downsides to working with small tanks. Parameters can just go out of control much faster than when there’s a larger volume of water. 

I didnt check the waters temp before adding it, but it seems like that may be one of the only possibilities. It didn't seem to be all that different though. 

I did add the dechlorinator. 

I've tested the water before and it was fine. It's well water so I don't think it would be subject to the same sudden changes that big water plants might make for city water. 

And I've never heard of "gassed off" water? Do you mind explaining it it's not too much of a hassle?

 

As for the fish, no changed from the guppies but the remaining cories are still acting happy as clams. I don't know why one suddenly died. 

[Maggie]

When you have cold water under pressure from the tap, it can hold additional atmospheric gasses (nitrogen and oxygen) that "gas off" upon aging. Here is a photo of a gallon jug one day after I filled it. Once I shake this jug, the bubbles dissipate to the top and there's a slight "pop" when I take the top off (like a soda). I don't fill them all the way to the top, as that helps the bubbles dissipate faster. 

[Fish Folk]

2 hours ago, Maggie said:

When you have cold water under pressure from the tap, it can hold additional atmospheric gasses (nitrogen and oxygen) that "gas off" upon aging. Here is a photo of a gallon jug one day after I filled it.

That's a very cool illustration Maggie! Yeah, I've had this question recently, and posted a thread about it. It's buried on the forum now someplace. Like Maggie says, especially when water is coming in from the cold, it can hold a lot more gasses. If you've read through many older books on the aquarium hobby, the expressions "let your water age" or "let your water rest" comes up. Serious aquarists used to do this all of the time: they'd draw water from their tap (be it well or city source) and let it sit open in a container for 24-72 hrs. Some will also add an airstone. The idea is that this gives the water time to "gas-off" the extra atmospheric gasses in bubble form before adding to your aquarium. Additionally, it allows chlorine / chloramine to vent off as well. 

In all honesty, we've never really done this. And many advanced aquarists don't either. The use of dechlorinator chemicals (Prime, et al) has made most of us a tad _lazy_ in this regard. What you'll find though is that if you do a BIG water change, sometimes fish get "the bends" -- where those tiny bubbles that hover around in the tank like a dust cloud in an old basement -- give fish something like the bends that divers get. 

Honestly though, from all that you're describing, I'm still puzzled. You didn't do a particularly huge water change. All I can think of is that something related to the small volume of water held in a 5 gal. may be at root. Gassing off may not be at all a solution to what happened. But it's at least something to bear in mind. 

Edited January 5, 2021 by Fish Folk

[Maggie]

@Fish Folk, I have old pipes (house built in 1950) and was originally more concerned about how to heat the water if I used a python, due to concern about metals possibly leaching in the hot water pipes. I do a small water change (10% - 4.5 gallons in one tank and 2 in another) in my main tanks 2x a week, and 20% 2x a week in the quarantine tank, for ease of handling the water jugs. It really takes only about 15-20 minutes to simply change the water if I'm not also gravel vacuuming, and that includes heating some in the microwave and mixing in a bucket, adding to the tank about a quart at a time, and refilling/dechlorinating the jugs. I know it sounds like a silly, over-reacting process, but it works for me in my very small house with only 2 sinks nowhere near a fishtank. I also tried 3 gallon jugs and love them but cannot handle one easily with one hand. It makes sense to have a python if you have a dedicated sink/fishroom and several tanks or large tanks, but it would be more of a pain in the butt IMHO to dry and store a 25 foot hose when you only have 2 or 3 tanks and a small home. I should add, too, that taking care of my aquariums is very mentally (and physically) therapeutic, so I don't mind any extra time it takes.

[Fish Folk]

Yeah, if it’s therapeutic and you don’t have too many tanks, that’s brilliant! 
 

we bought long heater hose extension to make our python stretch ca. 35 - 40 ft. We just let algae grow a bit in the hose 😂

[gardenman]

With well water you can have wild swings, especially in shallow wells. My well is only about twenty feet deep and the water quality can vary wildly. If you've got a deep well in a very large aquifer you'll experience fewer fluctuations, but even then there will be some variation. My well water has a very high iron content, low ph, high ammonia, and nearly no calcium hardness. I keep aragonite in my tanks/filters to add calcium hardness and boost the ph. I store the water in plastic jugs (old kitty litter bottles) and the ammonia goes down there. The plastic also absorbs a bit of the iron as over time it turns orange from the iron. I keep my tanks heavily planted and the iron is good for the plants. I can't do large water changes or I'd kill the fish, but this system works for me. My nitrates are always high, but that's good for the plants. In tanks where I want snails I'll add cuttlebones (the things used for pet birds) for the extra calcium. It works for me. The good news is no chlorine/chloramine, no fluoride, and I've learned how to manage the water.

[Lexi B]

@gardenman @Fish Folk@Maggie

Thanks for the explanation! While I can't say for sure, I don't necessarily believe that  unrested water was the issue. I'm still not sure what happened though. My boyfriend and I went back and looked over the water from the tap and nothing seems out of the ordinarordinary. 

As of now, no other fish have died. Although it's too early in the morning for me to know if the guppies are still behaving oddly, I'm hoping that the lack of other deaths is a good sign. 

It's just so strange to me. The pygmy cory that died showed absolutely no sign of distress and looked so healthy. 

 

I really appreciate everyone taking time to respond to me, though. I've only been doing this for a few months and was too anxious to reach out to other people. You all have been very kind and helpful though!

[lefty o]

1 hour ago, Maggie said:

@Fish Folk, I have old pipes (house built in 1950) and was originally more concerned about how to heat the water if I used a python, due to concern about metals possibly leaching in the hot water pipes. I do a small water change (10% - 4.5 gallons in one tank and 2 in another) in my main tanks 2x a week, and 20% 2x a week in the quarantine tank, for ease of handling the water jugs. It really takes only about 15-20 minutes to simply change the water if I'm not also gravel vacuuming, and that includes heating some in the microwave and mixing in a bucket, adding to the tank about a quart at a time, and refilling/dechlorinating the jugs. I know it sounds like a silly, over-reacting process, but it works for me in my very small house with only 2 sinks nowhere near a fishtank. I also tried 3 gallon jugs and love them but cannot handle one easily with one hand. It makes sense to have a python if you have a dedicated sink/fishroom and several tanks or large tanks, but it would be more of a pain in the butt IMHO to dry and store a 25 foot hose when you only have 2 or 3 tanks and a small home. I should add, too, that taking care of my aquariums is very mentally (and physically) therapeutic, so I don't mind any extra time it takes.

the trick to make sure nothing has leached into the water that goes into your fish tank is to run the water for a few minutes before putting any in the aquarium.  elements that can leach out of  lead/copper/iron pipes  only happens in any quantity when the water sits in the pipe. the flowing water wont get the bad stuff from the pipes. so run enough to flush out the water that has been sitting in the pipes, and proceed with water changes etc.

Edited January 5, 2021 by lefty o
dyslexic typing

[Lexi B]

Final update hopefully:

All of the fish are acting normal and happy again. No other deaths, no changes in water parameters. 

I don't know what that was, but I'm glad that the other fish came out unscathed 

[Lexi B]

Final update hopefully:

All of the fish are acting normal and happy again. No other deaths, no changes in water parameters. 

I don't know what that was, but I'm glad that the other fish came out unscathed