My Pet Fish Keep Dying?


New member
Jan 16, 2017
Very confused. I bought a 38 Gallon Tank and let it cycle for a couple of days. Then I went out and bought tropical, aggressive fish, so just seven. They were all advised to get from the guy at the pet store. One of the fish is a bit larger then the rest but they seemed to get along. I also have a heater in the tank, de-chlorinated the water and it's crystal clear with the 50 Gallon Filter I have running. I also got a catfish and two algea eaters.

One by one they keep dying. Not sure if its because there's a bully in the tank (eg the big blue fish). The reason I am confused-

1) The fish are not leaning on their sides- which sick fish do before they pass away. They all appear healthy. Then I come home and one is just dead on the gravel. No reason. No injuries.

2) The water is crystal clear. If there were issues with the water, wouldn't it be cloudy??

3) None of the fish are getting eaten- just fully dead.

4) I have a 38 Gallon and only 7 fish (now down to 3 plus the catfish and algae eater). They say the bigger the tank, the less maintenance. Plus I am not overcrowding them.

They did a water test at the store when I first got them, and the guy said my ammonia levels were a tad high. But that's normal for a cycling tank.

I think it's the blue fish bullying and stressing out the smaller ones out? Or perhaps the bigger algae eater (Pleco) - because I got him a week after getting the first algae eater (who was smaller) and the next day, the smaller one was dead. I'm upset I'm wasting money and losing fish. Didn't realize it was this hard.

The only other issue I think could be the heater? But it's always 80-82 degrees. That's normal I am told. I tried posting this earlier but it didn't work. I've gone on countless forums on the internet, but no one is answering :(

Any advice would help.


New member
Aug 3, 2016
On the Farm
Are the fish the same species or different? If you do a community type tank you are going to want to house fish that can actually get along with each other, and no I definitely doubt it was the Pleco, plecos are great for community tanks and so are corydoras. If you are new to raising fish I absolutely advise against doing a community tank of aggressive fish!

Also cloudy water isn't always a bad thing, there is such a thing as "bacterial boom" which is quite normal. You're gonna want some bacteria in there believe it or not, also you're gonna want to not keep it pristine all the time, it's best to do only like 25% or so water changes when you do change it, I mean yea you don't want grungy water but it's good to have some good bacterial growth if that makes sense.

I have a community tank that I have had for almost a full year now, it's a 30gal; a couple plecos, a few snails, like 7 corydoras since they prefer to be in a school of sorts, umm neon & glowlight tetras, and like 4 glofish. Some people do advise against doing a community with glofish (original black tetra before turned into a glofish) since they can be nippy, but I have had no real issues with mine. I also find that using things like fish medicines to keep the fins in good condition works well - all natural things like that.

So definitely find out what fish can be housed safely in a community tank, and again I would advise against housing aggressive fish especially if you're new to keeping fish.


New member
Feb 2, 2017
In all likelihood, your fish died because you didn't cycle your tank. 2 days isn't nearly long enough. It usually takes a new tank 4-6 weeks to properly cycle. Cycling your tank allows nitrifying bacteria to colonize in your filter media, substrate, and decor. It's this bacteria that breaks down highly toxic ammonia into less dangerous nitrites, and then breaks down nitrites into even less dangerous nitrates. In order to achieve this cycle, ammonia must actually be added to the tank a few times during cycling to give the bacteria a food source. Without this bacteria build-up, your fish were being poisoned by ammonia (fish only lay on their sides while dying due to a few specific diseases, not usually ammonia poisoning) that's produced by fish excrement and left over, decaying food.
If you got your fish from a big chain pet store, it's unfortunately likely than the sales person knew next to nothing. When your tank is finished cycling, you should have test readings of 0 ppm ammonia, 0 ppm nitrites, <40 ppm nitrates. Then, it's safe to add fish.
My advice would be to buy a test kit first. Test your water. Don't add any more fish until you can achieve these levels. Also, research the fish you'd like to add before you purchase them, or try to purchase them at an aquarium specialty store where the staff are more knowledgeable.
Large tanks are more stable once properly cycled, true, but a 38g tank is fairly small. You'll still need to do water changes weekly for the life of the tank.
Not what you wanted to hear I'm sure. Sorry about that. Aquariums aren't hands-free though; they require quite a bit of time and work to properly care for them.


New member
Nov 4, 2012
You have not cycled your tank.

"Cycled for a couple of days" was the problem.

Aquarium nitrogen cycle
can't be done in a couple of days. Not without a source of ammonia and heavy bacteria seeding anyway. If you had none of those two, your tank was not cycling at all. It only began to cycle once you have added the fish which started to produce ammonia. To cycle with fish, you have way too many fish, to begin with. You should have kept the bioload to a minimum. Now your fish have died one by one, and it is most likely because of ammonia poisoning.

If all your fish have died. I would suggest you do a fishless cycling with ammonia. It is quicker, and you won't risk losing any fish.

There are some tips to speed up the aquarium nitrogen cycle.


New member
Dec 31, 2018
I agree with Sherlar and Vash. Cycling properly takes a month or more. I waited 2 months for mine. You can speed things up by using Seachem Stability which helps with good bacteria. You should really have gone into it more before adding fish. Check your water with a Amonia, nitrate, nitrite test kit. They're worth the price to keep your fish safe.


Mar 22, 2021
I agree with everyone who has replied to this thread. In your post the only thing you said they tested was amonia which Isnt really your main focus when starting a tank. You should have bought and API water testing kit and tested PH, Nitrates, Nitrites, Amonia, and after testing you should have adjusted those as needed. I would like to know what kind of fish you got because 'Big blue one' isnt a type of fish. I would also like to know what kind of Pleco and catfish you got because if you got Common Plecos, they would have gotten about 12 inches long if they hadnt died. Im not trying to shame you, All I mean by this is that you should probably do a bit more research before you get fish. I made the same mistake, I got goldfish and I didnt know about the Nitrate Cycle so I tried to put Cory Catfish and Plecos in and they all died of amonia Poisoning (probably what some of your fish died from if you never did water changes) Another thing is that most Plecos dont eat alga, they are carnivorous catfish that will ocasionally snack on light algae. If you want a good algae cleaner I would suggest Hillstream Loaches, Rosy barbs, Otto Catfish and mainly plant eating pleco like Bristle nosed pleco (which still need meat) Also, no the water is not always cloudy when somthing happends in the water. I hope this helped though it seems like you already have some very good advice.


Mar 22, 2021
Its true that if the fish get hungry enough they will eat eachother but in this case i think its an issue with the water


Crazy fish lady
Dec 7, 2019
my fish used to eat other fish
It’s an issue with the water, not aggression. You can’t cycle an aquarium in 3 days, it’s not going to happen. The only way to do that is by filling up the filter with pre-cycled filter media. If you add an already mature colony of bacteria to the tank, then you can skip most of the cycling process.

And tbh, @Anna Loves Animals <3 keeping fish together that kill eachother is NOT good fish keeping. That’s like taking an aggressive dog and putting it with 2 week old kittens. I hate hearing “is just a fish.” Fish are animals just like dogs and cats.

Fish are by far the most mistreated animals because there is so much miss-information about them and they are sold at stores like houseplants. It hurts me when I see people treating animals like they aren’t a living, breathing creature that can feel pain.

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