Fish dying off one by one

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Birb06

Aquarium Advice Newbie
Joined
Mar 13, 2025
Messages
7
Location
Australia
Hi,
I have a 130 L tank that has up since end of December. It took a week to cycle as I used media and I tested the water and everything was perfect.
My current stock list is:
1 dwarf gourami
3 upside down cats
7 glass cats
4 bristlenose pelcos
3 Otto’s
1 ghost knife fish
(Yes this tank is highly stocked, but all fish are still baby’s and as they out grow the tank I will be upgrading)
Filter: aqua one nautilus 1100
Weekly water changes: 30%
I do not use a water conditioner as I use filtered tap water
I feed the dymax bottom feeder and flakes both pre soaked.

My current tank parameters:
Ph: 7.4 (high, but usual for Australian tap water)
Ammonia: 0
Nitrite:0
Nitrate: 0-5

My problem is every time I add an angel fish or blue ram, they die within two weeks. It first started with an angel fish. I acclimated him for 15 mins adding around a cup of water every so often and then let him in the tank. For the first few days he was fine, eating and swimming around. Then suddenly he stopped eating and stayed in a corner. I immediately isolated him and did a dewormer (flubendazole) on him in a quarantine tank and the main tank. It did not work and he started doing flips (I’m guessing a swim bladder problem) and died a few hours later.

The next week I bought another angel fish thinking the first one died because of a genetic issue, who looked bigger and healthier. He lasted about a week before going through the same issue again and then died a week after, flipping for a few hours and then dying. That time I treated with both the wormer again and melafix which didn’t work. At the same time I had a blue ram die of pop eye who I had for about two months. I didn’t think anything of it as he was injured the week before, close to his eye and I tried to fix with the melafix which didn’t work.

I decided to try one more time with the angel fish and I also bought a replacement blue ram. The angel fish fine again for a week and then started showing the behaviours again, so the fish shop where I bought him asked me to bring him in. At first he wouldn’t eat there in their quarantine tank but eventually he went back to normal and they are still holding him there for me. The blue ram was fine for the first few days, then one day I didn’t notice her at feeding time but didn’t think anything of it as she was small and hard to find, but the next day she was dead floating in the tank.

I thought that maybe the fish store I was getting them from was getting bad fish so I decided to go to a different fish store where I got a balloon blue ram. She lived a week and then stopped eating and was dead the next day. What I noticed though was that her fins were clamped and she was dulling in colour, so I tried to treat her with an antibiotic (TETRACYCLINE HYDROCHLORIDE) which again she started flipping and didn’t work.

In the few months that this has happened I have also gotten three glass catfish (one died). 3 ottos (no casualties). One ghost knife fish(no casualties)

What happened with the glass catfish was that I noticed her lower half was smaller than the rest so I just tired to make sure she ate which was fine for a few days, then suddenly she had scoliosis, lost her feelers and her fins were incredibly damaged and slowly lost her ability to swim so I put her down. Since then I have noticed that some of my older glass catfish are losing their feelers slowly.

No other fish are showing any symptoms only new fish. I feed my fish a varied diet of pellets, flake, frozen blood worms and live black worms. I have found when a fish is sick they will refuse all of them. None of the fish were bloated and poop seemed either a little stringy or normal.
It seems that the fish starve themselves to death, but I don’t know what’s causing them to not eat. I find it weird how they die in my quarantine tank but was fine in my the fish shops one. Please help I can’t kill anymore dead fish and thank you for reading.
 
Its sounds like there is something in the water that your older fish have gradually acclimated too, which newer fish introduced arent.

I would get a 2nd opinion on your water parameters. Even though your fish are young the nitrate is suspiciously low for your size aquarium, number of fish and your water change schedule.

I would get a chlorine test and check that the filter is removing chlorine properly. While a tap water filter should be removing chlorine maybe it's not working as efficiently as you think.

The filter media in most tap water filters will last about 150 litres before needing changing, which could be months if used just for drinking water as intended, but running water change water through it would only last a couple of weeks, so I would change the filter media with every 2 or 3 water changes to be safe. It's pennies for water conditioner compared to however much new tap water filter media costs though.

Water conditioner also removes things like heavy metals which your tap water filter doesn't. Unless your tap water filter is a 3, 4 or 5 stage RO filter rather than just a tap water filter like a brita that we have on our supply i would still use a water conditioner.

These tap water filters aren't as efficient as you might think, and with the volume of water you are putting through it, it probably isn't doing anything a couple of weeks after you replaced the filter media.
 
I agree with Aiken in that the fish are not acclimating to your water. The fact that the fish you returned went back to " normal", says it's your water that the fish aren't used to. Your acclimation method is too quick for the dying fish. You should be doing the slow drip method over the course of at least an hour or possibly longer based on the one fish's recovery. Here's how to do a drip acclimation: Acclimation Procedure for Aquatic Life: Welcoming Home New Arrivals).
You have a collection of fish that come from different water parameters which can explain why some of the fish do fine with your water and some do not.
I would definitely get a second opinion on your water parameters which should include metals like iron and copper. If it's well water, you may need to use an agency different from a pet store. (Stores which sell saltwater fish should have kits for testing copper and iron.) If it's water from a municipality, you should contact them for what is in the water.

As for baby Angelfish, I suggest not getting any under a nickel body size. There is a natural die off of baby Angels and that usually happens before they reach that size. The bigger the fish is, the more likely the fish is healthy and going to live. Smaller fish ( i.e. pea size, etc) are less secure by themselves so they should be in a school at least since they rarely do well alone. Balloon Rams are just disfigured fish so there are a whole bunch of internal issues all Balloon fish have. I would save your money and skip the ram, any ram, with the collection of fish you have as their needs are very different from your current fish's needs.

Hope this helps. (y)
 
You guys are actually life savers. I never would have thought that tap filters need to be changed so often. I got my water tested with a chlorine test and it measured off the chart. I have now bought some prime and have done a 50% water change using it and hopefully if everything goes well I’ll pick up the angel fish tomorrow.
I also had my water tested and it measured up the same as before, but I will keep an extra eye out with the prime now.
Thank you so much for both of your advice. :)
 
If nothing else, PRIME helps add back some slime coating which is very important to fish. Even if you don't use it for dichlorination, it's a good thing to add when doing water changes since you are adding " raw" water. (y)
 
They don't need changing all that often if you use them for what they are intended, which is for drinking water. My tap filter has an integrated tap. There is the normal hot and water lever on there, which bypasses the filter for general use, and a second lever which discharges drinking water that's gone through the filter. If you just use the drinking water lever for drinking water only the filter will last months, if you use the drinking water lever for everything the filter will last a few weeks.

Tap water filters like the ones brita make also have a water softener in there. Water softeners work on an ion exchange principal that replaces magnesium and calcium with sodium thus reducing general hardness while maintaining total disolved solids. Sodium isn't always good for freshwater fish, sometimes people get away with it, sometimes they dont. Fish that suit hard water will usually be ok in the presence of higher sodium, fish that prefer softer water may not do well. If you speak to Brita their advice is that you are probably going to be OK with using water that's gone through their filter, but they recommend you use the bypassed general supply not the drinking water supply for aquariums.

On a side note, if you arent changing the filter at all dont use the drinking water tap full stop. All sorts of bacteria will build up in the filter over time, and if it's not changed every few months this bacterial build up can be hazardous to your health. Im thinking legionnaires disease as a worse case scenario. If you arent changing the filter every few months you are better off just removing the filtration system and removing the health risk.

One thing to take from this is that fish can survive in chlorinated water to a degree. I found this because my nephew keeps a few platys, and they don't use water conditioners either. Their water supply isn't potable, but there is some chlorine in there. Say a 30% water change would leave about one third the level of chlorine in the aquarium compared to what's coming out of your tap, which will obviously be safer for fish than the full on concentration. And, if your aquarium has good gas exchange at the surface the chlorine should offgas in a few hours, so over the course of a day the chlorine should be all gone. Some of my nephews platys die and some don't, they breed and some fry make it while others dont. Survival of the fittest as he puts it. He's quite a determined kid and isn't going to take advice, so I let him get on with things.

If your water supply is treated with chloramine instead of chlorine, that's a whole different ball game.

Hopefully removing the chlorine will sort things out, it certainly won't hurt things. Let us know how things go and if still have issues we will have to look to another cause. On another point, blue rams prefer their water on the warm side, 28 to 30c, that may not suit your other fish which may have been a factor in them not doing well for you.
 
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