My fish are slowly dying. :(

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Apr 7, 2021
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Buffalo Grove, IL
First, I want to say that I am by no means a tank expert. I have had tanks in the past and never had a problems but also never really needed to do anything besides regular maintenance. This new tank though has been a bit challenging. Heres whats going on:

I bought a 65 gallon tank back in the beginning of January. I started with an over the back filter because it was part of the package that I got. The person at the fist store assured me that the filter was more than good enough to maintain the tank. I have 2 bubble stones because bubbles and a power head for circulation. The power head is for a 55 gallon tank but with the over the back filter I figured it was good enough for circulation/aeration.

I added some plants, and some decorations. (a large ceramic "log" in the middle of the tank and some plastic plants) I added the water and the starter treatments and then let the tank do its magic for about a month. (my 6 year old was not happy because she wanted fishes in the tank immediately). I did regular water tests and everything was looking good.

After the month was over I took a water sample and went to the aquarium store. They tested the water and said everything looked good so I picked up 8 small community fish and a pleco. I let the kid pick and she wanted 4 Rasboras and 4 Gouramis. Two weeks later we also went and got a few fancy guppies because the kid wanted them.

Everyone was happy, the tank looked great, the fish seemed healthy and regular water checks were showing everything was good.

Then, the guppies died off one by one. Not sure why, water tests again showed everything was good. So I started weekly 25% water changes. Then one gourami died, and a week later the second one died. Then the pleco literally disappeared one night. Seriously. Its nowhere. Checked everywhere. Its just gone. It was bigger than all the other fish so there is no way they ate him in one night.

So I talked to one of the fish geeks at the pet store. He suggested maybe trying a better filter. The tank is a tall tank so maybe the over the back filter isnt doing a great job. So I picked up a canister filter and set it up. Other than it being loud (not the canister, but the water spraying from the output nozzle) it seemed to be working well. A few days later, another dead gourami.

I really dont know what im doing wrong. I feed them 3 times a day but sparingly as to not overfeed. I also give them 2 different kinds of food. (bug bites flake, and some dried worms)

Other than some sort of disease, I dont know what it could be that is killing the fish.

Any help would be appreciated.
It sounds like your tank has not cycled.

You say you put in starter and then left it for a month, but without an ammonia source the bacterial starter has nothing to feed on and will not populate your filter media.

When you added the fish you essentially started a fish in cycle, and without daily water changes that can go the way you are currently describing.

When your fish shop tested your water it will of looked perfect because there was never any ammonia, so that never turned to nitrite or nitrate.

This thread should help you out.

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You are doing too much too fast.

The HOB filters that come with tank kits are usually good 'nuff for most things they come with, unless it was a larger tank. They get optimistic above 55 gallon sometimes. Changing to the canister will cause issues, unless you also leave the HOB filter up for a bit with it. The nozzle shouldn't be making noise, as it should be submerged, unless you're looking for that waterfall noise.

I didn't see a tank size, but adding that many fish that fast is not only going to stress the fish, it will cause spikes all over the place. Not sure what testing kit you're using, but I can almost assure that there was at a minimum an ammonia spike. These 2 things cause more fish to die with new tanks. Stress and ammonia. Add in not a huge colony of BB established yet, and you got a recipe for bad things to happen.

My advice is to stop adding fish. Do not change the filter again. Allow the tank to recycle with the new filter with the fish in there. You may lose more even. The pleco may have just buried itself. They do that. Watch at night. They sometimes only come.out at night. Especially stressed. Small water changes for a bit. Minimal feeding, meaning skip a day and feed every 2 days for a while.
I havent added any fish for a while. I didnt want to kill anything else. I have the basic Tetra testing strips at home and I was using those daily for a while to see where the tank was at. The fish store has a different testing method involving different tubes and droppers and stuff. They said the water was good to start adding fish, otherwise I would have waited. :(

The HOB filter was rated for a 65 gallon tank (I have a 65 gallon tank), but I honestly didnt think it was going to be enough from the start. Once again, the people at my local fish store are the ones that recommended it. They told me I didnt need to buy a canister filter. When I was there to buy my equipment they didnt have a canister in stock that was the right size for my tank so I think they just wanted to sell me something. I had said I might order a canister from amazon or something and the owner of the fish store talked me into the HOB filter. I did leave the HOB up for almost 2 weeks when i changed to the canister. My buddy told me that should be long enough to transfer bacteria to the canister.

The pleco - no idea. After a week of not seeing him, I did dig around in the substrate during a cleaning to see if he buried himself and died, but didnt find him in there.

I am wondering if I am overfeeding. I give them a really small amount of food when I do feed them and none of the fish have big bellies so Im not sure if im doing anything wrong, but I can go to a once a day feeding or even every other day if you dont think that will starve the fish?

I also forgot to mention that I did also add a few live plants. They are doing well. Not sure if that helps with the advice, but thought I would mention it.

My tank did have some ammonia according to the tests. it was showing that it was in the safe zone, but did show that there was some ammonia in the water.
My tank did have some ammonia according to the tests. it was showing that it was in the safe zone, but did show that there was some ammonia in the water.
Ammonia should be zero. Any amount of ammonia will harm the fish. Reading the above recommended thread will help with understanding how to cycle the tank.

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