Fish all dead - need advice

[Should have got a puppy]

Possibly the wrong thread to post on, as I have no living fish any more. All 9 died in the last two days and I am really upset.

Bought the tank in Aug (60 litre), left it a couple of weeks with some wood and plants from local fish shop, couple of weeks later added a couple of Neon tetra, and then a few weeks later a couple more, and again until we had 6.

They looked healthy, but I felt they were not happy, because they just didn't swim around that much unless it was feeding time, so I didn't get any more for a long time as just thought they needed time to settle. My dad has kept tropical fish for years, and told me it was all in my head, and that the fish were happy, but as I wasn't so sure, I just didn't buy any more. Then one day, I thought the water temp felt a little low on my skin, so bought a thermometer and the water was cooler than the thermostat was set at - I'd set the thermostat at 25 and the water was about 22. So I turned it up, until the temp was reading 24C and the fish perked up, and finally I felt ready to buy some more fish.

So I bought added a few Molly's, and they all looked really happy, and I felt very happy with the tank.

Then, a few days ago, one of the Molly's was hanging out at the bottom, which I thought was a bit strange. I went to work, and came back and found all the neon tetra dead. The Mollys looked okay. I then checked the temp and realised then water was only 20-21C. It had been a bit of a cold snap and In a bid to save the fish, I added a few litres of tap water, boiled and allowed to cool - with some tap safe, but perhaps a few degrees warmer than the tank water, in a hope it might raise the temp until I could get a new thermostat. I turned the thermostat up to 31C and the water temp came up a little to 22C.

I tested my water - nitrites, nitrates, ammonia all zero. pH 6.5.

Next morning, the Molly's were all dead.

Could it be the temperature alone that killed them all? Or the shock of me adding slightly warmer water?

Do I need to empty the whole tank any clean everything, in case it was a disease, even though I didn't see any evidence of anything?

If I do need to clean the tank, what do I clean it with?

Thanks in advance.

We were going to get a puppy, but our kid wanted a fish. I thought it would be easy.....

 

[Colin_T]

Hi and welcome to the forum.

The low temperature is unlikely to kill the fish. Most tropical fish have seasonal changes in temperature and neons live in water that might drop to 16-18C and go up to 28-30C. Same deal with mollies.

The low pH (6.5) is too low for livebearers like mollies, platies, guppies and swordtails. These fish do best in water with a GH above 200ppm and a pH above 7.0.

The pH is unlikely to be what killed the neons because they naturally occur in acid water (pH below 7.0).

It sounds like the heater is dodgy and malfunctioning. You could also have a dodgy thermometer and maybe you cooked the fish. These 2 items need investigating.

For all the fish to die within a short space of time it is usually a water quality problem like ammonia, nitrite, or something toxic got in the tank. Without pictures it's hard to say. It can also be heat if the heater malfunctioned and the water temperature went too high in a short space of time, the fish could die.

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I would get the heater tested and take the thermometer to the shop and compare the temperature to other thermometers there. If there is a difference between yours and the ones at the shop, maybe you have a faulty thermometer.

Then I would gravel clean the substrate and drain the tank. Then refill it with dechlorinated water. Let it run a few days and add a small group of cheap fish (maybe 5 or 6 neon tetras. Leave them for a month and see how they do. If they get sick, post pictures and video straight away.

 

[Should have got a puppy]

Thank you so much for your reply.

Hi and welcome to the forum.

The low temperature is unlikely to kill the fish. Most tropical fish have seasonal changes in temperature and neons live in water that might drop to 16-18C and go up to 28-30C. Same deal with mollies.

The low pH (6.5) is too low for livebearers like mollies, platies, guppies and swordtails. These fish do best in water with a GH above 200ppm and a pH above 7.0.

The pH is unlikely to be what killed the neons because they naturally occur in acid water (pH below 7.0).

It sounds like the heater is dodgy and malfunctioning. You could also have a dodgy thermometer and maybe you cooked the fish. These 2 items need investigating.

For all the fish to die within a short space of time it is usually a water quality problem like ammonia, nitrite, or something toxic got in the tank. Without pictures it's hard to say. It can also be heat if the heater malfunctioned and the water temperature went too high in a short space of time, the fish could die.

----------------
I would get the heater tested and take the thermometer to the shop and compare the temperature to other thermometers there. If there is a difference between yours and the ones at the shop, maybe you have a faulty thermometer.

Then I would gravel clean the substrate and drain the tank. Then refill it with dechlorinated water. Let it run a few days and add a small group of cheap fish (maybe 5 or 6 neon tetras. Leave them for a month and see how they do. If they get sick, post pictures and video straight away

Thank you so much for taking the time to write such a detailed reply.

The water definitely felt cold, and the thermometer was correct, as I also checked it with our cooking thermometers. I don't think the tank temp ever went up high, but I may have shocked the fish adding the 2 jugs of slightly warmer water - though the neon's were already dead at this point.

Because the water tested negative to ammonia, nitrites and nitrates, I wonder if there could have been a disease that would affect the fish this quickly that I didn't pick up on? I took a picture of the last dead Molly, but wasn't sure if it was appropriate to post a photo of a dead fish on here.

 

[Colin_T]

If there is a problem with your fish, then post pictures of any living fish and any recently dead fish. Sometimes we can see something on the dead fish that helps work out what is going on.

Even though this is a family friendly fish forum, we do sometimes have to show dead fish and we talk about fish poop too. So if you have pics of the dead fish, post them.

 

[Should have got a puppy]

The last of our 9 fish to die.

 

[Colin_T]

The fish looks ok (besides being dead) so we go back to the tank.

Did you do anything (water change, clean filter, etc) to the tank on the day the first molly died or a few days before it died?

What did you feed them?

Do you have buckets, sponges, hoses, etc, specifically for the fish?

Do you use any sort of anti-bacterial soap or hand wipes with disinfectant on? These can leave a residue on your skin that can get into the water.

Did you have visitors just before the fish died?

 

[Should have got a puppy]

Thank you Colin.

No water change or cleaning filter within a couple of weeks of the fish dying. I'd possibly added a jug or two with a little tap safe maybe a couple of weeks before.

I'd cleaned the glass a little with our tank sponge on a stick within the week that they died. It wasn't terribly dirty though. I did also remove and rinse the two live plants with tap water, to remove a bit of algae on the leaves, but they were almost air dried before I returned them - do you think this could have been the reason?

We use regular liquid hand soap - nothing advertised as specifically antibacterial (Palmolive I think we have at the moment). I would normally make sure my hands were clean before putting them in the tank to clean it, but would rinse well and dry well too.

I feed them a very small pinch of Aqua Care Tropical Flakes with Mealworm every day, usually once a day. Occasionally twice if the kid begs to feed them and I've already done it. Very occasionally I miss a day of feeding - as I'm sure I read somewhere that can be good?

The 6 neon tetra were bought back in Aug/Sep. The 3 Mollies mid Dec. They all died a few days ago over a 48 hour period.

 

[Colin_T]

cleaning the algae off the glass did not cause this unless there was something on the sponge.

it is fine to leave fish to go without food for a day, it doesn't affect them.
it's good for people too.

the other thing that might be happening is the driftwood is leaching something into the water. Maybe take that out for a few months and see if the new fish do ok. If they d, then add the wood and monitor them. In the mean time, the driftwood can be hosed off each week and put in a bucket of water outside. Change the water each week when you hose it off.

 

[Oblio]

We use regular liquid hand soap - nothing advertised as specifically antibacterial (Palmolive I think we have at the moment). I would normally make sure my hands were clean before putting them in the tank to clean it, but would rinse well and dry well too.

Just to be sure (so the problem can be fixed), you are speaking here of using soap to clean your hands and then hands well rinse well, not the tank or anything put in the tank.