1 fish dying each day

hi, I have a 50 gallon tank, which has been fishless cycled for the past month. I introduced 2ppm ammonia until the water parameters were able to absorb ammonia and nitrite in 24hrs. Then I adjusted to 3ppm (for assurance) and that was successful too. I then added 16 fish to my aquarium on the 30th June (6 endlers and 10 Platys). So far I’m left with 10 fish remaining and it’s been less than a week.

Tested the water parameters today:
Ph - 7.6
Water temp - 78 degrees Fahrenheit (26 Celsius)
Ammonia - 0.0ppm
Nitrite - 0.0 ppm
Nitrate - 10ppm

I’m unsure what the hardness is.

I did a 50% water change the morning of the 30th June and got nitrate to below 10ppm. I introduced the fish in the afternoon. I did a drip acclimation for 45 minutes. I use seachem prime to condition the water. This aquarium is at my parents house and I go over every second day to monitor water parameters and conduct any maintenance. My mother feeds the fish twice a day (morning and night).

I live in the southern parts of Australia and currently it’s winter. The aquarium is set outside under the patio. Currently temperature reach 48 degrees Fahrenheit at night and 60 degrees Fahrenheit during the day. I use a fluval 300w heater to heat the tank.

Can anyone please give me advice on what I might be doing wrong? Below is a picture of a platy I found today. I Cannot see any signs of wear on the fish but then again I’m a novice and probably missing something.

Also this aquarium does not have a lid, was given to my parents from a friend. I use a sand substrate that was also provided. I rinsed the substrate, sand and canister filter thoroughly before use.

A few questions so that we can understand the problem better. Your tank is outside where the temp drops to 9C at night and 16C during the day. You mentioned that the water temp is 26C, is that during the day only or it’s also 26C at night? The 300W heater may struggle to raise the temperature of a 50G tank by 17 deg C at night.

You said you are in the southern part of Aus. Is it the South east of the country (VIC), south-central (SA), or Southwest? Vic typically has quite soft water (Low GH) while SA could have quite hard water (high GH). Although this is important for the long term health of the fish, it shouldn’t kill the fish in a few days.

Is the aquarium which is under the patio gets direct sunlight during the day which could raise the temp substantially or is it protected from direct sunlight?

I can think of only 2 things at this stage, high fluctuations of water temp during day and night or there’s something in the water (other than pH, GH, Amm, Nitrite and nitrate) which is detrimental to your fish.

If you can post a photo of the whole tank showing everything in it, it would help.

Which fish died?
16 fish is a lot of fish to add right when it’s done cycling… normally you should only add a few at a time… that many fish could’ve overloaded the bio load, but if the temperature is fluctuating, that’s more likely to kill the fish in days.

Hi TNG, thanks for the information. I have yet to see the temperatures at night. So cannot provide an answer on that. However the tank is located under a roof with shelter so no direct sunlight hits the aquarium. I’m located in Adelaide and was made aware from my local LFS that our water tends to be more hardier than other states. I do have a spare 100w heater lying around (unsure whether it still works) but was thinking of putting it in the tank to help ease with any temperature shock. I’m going over to my parents house tomorrow night for so can assess the temperature at night and will also attach a photo. Again thanks for the response.

Lillypad101 said:

Which fish died?
16 fish is a lot of fish to add right when it’s done cycling… normally you should only add a few at a time… that many fish could’ve overloaded the bio load, but if the temperature is fluctuating, that’s more likely to kill the fish in days.

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So far have lost 3 endlers and 3 Platys. I have an API test kit and checked the water parameters. Everything seems to be normal as in no ammonia spike seen and nitrates haven’t increased a whole lot since the 30th. I did conduct a 25% water change today but that was more to make my life easier knowing I’ve done it. Nitrate was at 10ppm before the water change.

Vjfish said:

water tends to be more hardier than other states.

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That should be fine, you have livebearers and they prefer a little harder water, do you have a picture of the tank? is it planted?

Lillypad101 said:

16 fish is a lot of fish to add right when it’s done cycling… normally you should only add a few at a time…

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At the end of a fishless cycle using ammonia there are (or should be if the cycle has been done correctly) enough bacteria to support a tankful of fish.
It's fish-in cycling, and plant cycling if the fish keeper is not totally happy with his plant growing skills yet, where fish should be added a few at a time.

The OP here did a fishless cycle with ammonia, so all the proposed fish can be added as soon as the cycle is complete.

None of us knows what "harder" water may be, so can you get the number. Check the website of your municipal water authority if you are on city water. We need the number and their unit of measurement. This is unlikely to kill fish this quickly, but you need to know the GH as it can have long-term detriment to fish depending what it is and the needs of the fish.

Temperature fluctuation is very important, and must not be more than a couple degrees diurnally. Temperature drives the metabolism of a fish, and they cannot take huge swings. And as someone mentioned, heaters are not made to increase the water temperature more than about 10 degrees from the air temperature where the tank is positioned. Over-worked heaters fail more rapidly, if they even work.

Test the source water on its own for nitrate to confirm it is clear of nitrate (or not, as the case may be). Nitrate should be as low as possible. Here again, nitrate at 10 ppm or 15 ppm is not going to kill fish like this, but it will slowly weaken them making them more susceptible to other things. If the source water is zero nitrate, then reducing the nitrate occurring in the tak is easy--water changes, vacuuming the substrate to remove organics, keeping the filter clean, not overstocking and not overfeeding. And live plants (floating are most effective here) to take up most of the ammonia/ammonium which means significantly less nitrite and nitrate resulting when plants use the ammonia/ammonium.

Turning to other possibilities...something in the sand, since it came from an unknown aquarist. If this dying fish continues, I would be inclined to tear the tank down and discard the sand. Play sand is inexpensive. You don't mention the filter media, but if this came from someone, throw it out. Clean the filter housing, you can use a mild bleach solution, then rinse very well and air dry. Add new media.

A tank cover is wise, to keep water in and other "stuff" out.

Pictures of the remaining fish and one of the entire tank?
Did you dechlorinate the tap water before using it in the aquarium?

Can you clarify the water temperatures for us?
You don't want fluctuating temperatures and unless the fish came from cold water tanks, they will be unlikely to survive a cold night outdoors.

I would move the aquarium indoors, even if it's into an outside room with a door, it would be easier for the heater to keep things warm. You should also insulate the base back and sides of the tank with 1-2 inch thick polystyrene foam. Just tape the sheets of foam to the outside of the tank to insulate it.

Put a coverglass on the tank to trap heat. Use 4, 5 or 6mm thick glass because it's less likely to chip compared to 2 or 3mm thick glass commonly sold in pet shops.

Hi everyone, so visited my parents place. Another 3 fish unfortunately did not survive. I have added another 100w heater to the tank to support the current heater. We will be moving the tank in the house this weekend. I have attached photos of the aquarium as suggested. Sorry for the poor photos.

In terms of how I condition the water. I put a capful of prime into the tank before I add any new water and also add half a tea spoon the the breeder box as I use that to break the flow of the hose and not to disturb substrate. I also use the sink tap to adjust temps close enough to the tank temp to not put the fish in any sudden shock. I will be going over my parents house later tonight to check the water temps at around 10pm local time.

Lost all but one small female Endler and 6 remaining platys.

Again thank you all for commenting and provide some helpful tips. I’ll get a Hardness test kit tomorrow to give a further update.

Also here is a photo of the 3 fish today that didn’t make it.

I can't see anything wrong in the photos, but other members probably could, so I leave it to others to comment.
The air temperature is usually coldest between 5am & 7am, so perhaps your parents could read the thermometer for you early in the morning.

The tank is near a brick wall, which will radiate cold onto it.
No coverglass and the heater will be struggling to warm the water.
You can put some glad wrap on the top of the tank to help trap heat. It won't trap a lot but might help. Just open the top each day for 30 minutes to let some air in then seal it up again.

There is blue green algae (bga, aka Cyanobacter bacteria) on the substrate in patches. Don't bother feeding them when it's cold, they won't eat and the food will encourage bga.

Is there any filtration or aeration?

If you have a 40 litre plastic storage container that is clean and free of chemicals, I would put the fish in that and take them inside so the temperature is more stable.

Colin_T said:

The tank is near a brick wall, which will radiate cold onto it.
No coverglass and the heater will be struggling to warm the water.
You can put some glad wrap on the top of the tank to help trap heat. It won't trap a lot but might help. Just open the top each day for 30 minutes to let some air in then seal it up again.

There is blue green algae (bga, aka Cyanobacter bacteria) on the substrate in patches. Don't bother feeding them when it's cold, they won't eat and the food will encourage bga.

Is there any filtration or aeration?

If you have a 40 litre plastic storage container that is clean and free of chemicals, I would put the fish in that and take them inside so the temperature is more stable.

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Unfortunately don’t have a container or any aeration tools (air pump, smaller filter to keep the water filtered and aerated).

I’m using a canister filter currently filtering 1100LPH.

I can’t see any signs of BGA or any algae.The picture quality is not the greatest and the substrate is a sand base that is mixed with white, black and grey particles.

Currently is around 9:20pm and the temperature of the water is 27C (80F). I’ll get my mother to check the temps at 5 in the morning before she leaves for work to work out the drop in temperature. Fish are eating and actively swimming along different columns of the tank. No signs of fish gasping for air.

your power bill is gonna be huge