Murder Mystery: Fish deaths after water change

maadi

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My tank is about 120 gallons and has been established for several years. Two weeks ago I did 2 water changes of about 25%, using Seachem Prime to treat the tap water. Last week, I did another 25% with Prime, and also added some Seachem Pristine and Stability, which I occasionally add with water changes. I remember shaking the bottle of Prime before adding it but am not so sure I shook the other two bottles first, as I usually do. It was the bottom of the Prime bottle. Expiration dates on the bottles are 2023-2024. I did forget to plug the water heaters back in, but the evening wasn't cold.

The next morning (just as I was about to go out of town!), over half of the fish had died. I quickly removed the dead ones and did another 25% water change, using Seachem Safe (about 1/8 teaspoon), because I was afraid to use anything I'd just used the day before. A couple of fish floating at the top suddenly swam away when I tried to remove them, and have survived the week. Malaysian trumpet snails appear unaffected.

After finding the dead fish, I was scared and in a rush to change the water as quickly as possible, so I didn't test the water. One week later, before the latest water change, ammonia was <0.25, pH about 8.3, nitrate about 5, nitrite 0. Then I did another 25% water change with Seachem Safe.

What went wrong?

Did my possible failure to shake the Pristine or Stability bottles add something toxic? Did the water change possibly stir up methane or other toxic gases in the substrate? Did the tap water possibly contain higher than normal chemicals? Temperature change? Something else entirely?

I'm afraid to kill off the surviving fish with each water change.
 

Alice B

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around here chlorine levels fluctuate. I use a simple dechlorinator that doesn't affect test results so I can double dose it. I've had fish act like a chlorine spike when I didn't... Had 3 die on a pond before I added extra chlorine remover last fall
 

jams

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Tough to figure out the culprit.
A couple of years back, I did my weekly 50% water changes on my tank 55 Planted community. Everything went normally but then about 1-2 hours later noticed everyone gasping at the surface. Without testing I immediately did another 50% water change. Everyone started swimming normally. Only theory's I have is that periodically since the water is pulled from Lake Erie which is known for algae blooms in the summer, the water company treats at a higher level or the fire dept flushes the hydrants. After that episode I always monitor the tanks for at least a couple of hours. Also, now I do double dose the tanks with Prime, just to be safe. Has not happen since.

Good Luck!
 

jaylach

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Tough to figure out the culprit.
A couple of years back, I did my weekly 50% water changes on my tank 55 Planted community. Everything went normally but then about 1-2 hours later noticed everyone gasping at the surface. Without testing I immediately did another 50% water change. Everyone started swimming normally. Only theory's I have is that periodically since the water is pulled from Lake Erie which is known for algae blooms in the summer, the water company treats at a higher level or the fire dept flushes the hydrants. After that episode I always monitor the tanks for at least a couple of hours. Also, now I do double dose the tanks with Prime, just to be safe. Has not happen since.

Good Luck!
I grew up east of Cleveland in the Eastlake/Willowick areas. In the spring and fall you could actually taste the algae in the tap water.
 

Colin_T

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I've said it hundreds of times and will say it again. Always dechlorinate new water before adding it to the tank.

Water companies are always playing silly buggers with the water supply. If they do work on the pipes, they add more chlorine/ chloramine. If there is excessive rain or hotter weather, they add more chlorine/ chloramine. When they flush the pipes they add more chlorine/ chloramine.

Adding straight chlorinated water to an aquarium always has the risk of poisoning fish.

Any new water should be free of chlorine/ chloramine before it's added to the tank.

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If you use a garden hose to fill the tank or water holding containers, turn the tap on and let water flow through the hose for 5 minutes before collecting the water. This washes out any hose softening agents that might have leached out of the hose.
 

GaryE

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Water supply pipes need to be managed as scale builds up on their inside walls. In Montreal, we'd have 2 treatments a year, and if you changed water the next morning or during the process, you could lose a tank. The chemicals used were said safe for drinking, but they slaughtered fish. I think they caused a massive change in alkalinity.

You could be dealing with something similar. We had a schedule and advance warning (after a while and many complaints, since it also affected clothing in washing machines) but I had a sad day of disaster when I did my water changes in pre-warning times.
 

Slaphppy7

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You don't need the "Stability" or "Pristine", all you need is the Prime...the more chemicals we dump into our tanks, the more we complicate matters

Did you match the tap temp to the tank temp as closely as possible before refilling the tank?
 

Alice B

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Any new water should be free of chlorine/ chloramine before it's added to the tank.

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If you use a garden hose to fill the tank or water holding containers, turn the tap on and let water flow through the hose for 5 minutes before collecting the water. This washes out any hose softening agents that might have leached out of the hose.
Can you suggest a good fish quality chlorine test? I think API used to make one, but I have not seen one for sale anywhere. And a pool kit is not sensitive enough
 

Byron

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I wouldn't waste money on a chlorine test. Following Colin's advice. But aside from that, chlorine issues are usually apparent immediately. Chlorine burns the gills, and fish will be gasping at the surface at the opposite end of the tank from the fresh water entering, and their gill covers will be extended and the gills red. Very noticeably so.
 

Alice B

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I take care of other people's ponds with thousands of gallons of water. I dump in a LOT of chlorine remover and drop a hose in. I have the fish in tanks while I fill but I would love a good chlorine test before I put those fish back in. Right now I am not double dosing chlorine remover, I am using 4 times recommended amount. With my chlorine remover costs, I think I could swing a $20 test and SAVE money.
 

Byron

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I take care of other people's ponds with thousands of gallons of water. I dump in a LOT of chlorine remover and drop a hose in. I have the fish in tanks while I fill but I would love a good chlorine test before I put those fish back in. Right now I am not double dosing chlorine remover, I am using 4 times recommended amount. With my chlorine remover costs, I think I could swing a $20 test and SAVE money.

You do not want to be using more dechlorinator than is necessary. Fish live in water, not chemical soups. I know all manufacturers will say that overdosing does not harm fish, but this simply is not accurate. Any chemical added to the water will likely have some negative effect on fish. Fish drink by taking in water via osmosis through their cells. Anything dissolved in the water that is able to diffuse across cell membranes (not every chemical is, but then there are other problems) will thus enter the bloodstream. This is why hard water is so harmful to very soft water fish--the calcium in the water enters the fish and blocks internal organs, esp the kidneys, slowly causing death.

Quality dechlorinators work instantly and effectively, so there is no need to over-dose. I know, most of us have the habit of thinking more is likely better, but with chemicals added to an aquarium this is far from true.
 

Alice B

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some of the water supplies I work on, I err on the side of safety. And simple dechlorinator, with only sodium carbonate and sodium thiosulfate is safer to double dose than more expensive brands with LOTS of chemicals. If I can't have a chlorine test, I have to overdose. Or I have dead koi and no business. Which means no house, no groceries... and no fish.
 
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maadi

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Thank you all for your thoughts. Though each water change now causes me a lot of anxiety and paranoia, hovering over the tank to search for any signs of distress, the survivors have survived multiple water changes since the great tragedy.
 

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