5 Gallon Tank Killing Fish

[FishRBeautiful]

For my 5 year old daughter, I have a 5 gallon tank with a glass lid (the kind that folds in half a little to feed the fish). It was mine and I don’t need it anymore. Now, Every fish we put in there dies. This time it killed a perfectly healthy betta she was excited about that came from a tank, not a cup at the lfs. When I was using it before, I didn’t know much about fish care so I had an air pump only. Then, I found out you need a filter so I got a sponge filter. Then I found out you’re supposed to clean your sponge filter. LOL (I’ve only been fishkeeping for a year so I’m learning a lot.) If I remember correctly, it maybe started smelling stagnant at the end of my using that tank when I opened the lid 

I stored the tank for maybe a few months. Now, I have a heater and sponge filter in there again. I did like an 80% water change before getting the betta and someone advised I put a carbon filter in to remove toxins, which I did, but it still killed the new fish. It always smells when I open the lid. So do glass lids make water stagnant and kill fish? I have an unused 10 gallon with a glass lid I plan to set up after my surgery also so I want to avoid this situation. Should I cut out the back and put an HOB in it? I have one
 

I’ve done water tests. It’s always like 0 nitrites and ammonia, 10 nitrates. Hard water as always. No chlorine ever. Never used bleach or dish soap. Could it be the pet store rocks? I don’t use those in my tanks. I use stuff from hardware stores for my substrate. I can’t remember where I got her rocks, WalMart, Petco, or PetsMart. If WalMart, can that kill fish? I don’t want to keep buying fish and have them die.  

[MattyM]

Are you sure the tank is cycled? How long before the fish die, and what does a test strip show then? Any live plants? What's the temp? Do the fish act or look any differently before they die? Eating and what not? What are you feeding and how much? Got any pictures? 

Sorry for the all the questions but these these are the kind of details we need to provide any help.

[FishRBeautiful]

I’ll get pictures and info later when I’m home. 

[AllFishNoBrakes]

All great questions by @MattyM. While I don’t know what the issue is, I can tell you for certain that it’s not the lid itself. I have lids on all 14 of my tanks and they’ve never been an issue. 

Edited March 11 by AllFishNoBrakes

[MattyM]

On 3/11/2024 at 1:20 PM, AllFishNoBrakes said:

I can tell you for certain that it’s not the lid

Have to agree - I've only ever had lidded tanks and never had any issues or unpleasant odors, even on my small 9g tank with just a sponge. 

[Tony s]

Honestly, it’s the smell that has me concerned the most. Shouldn’t be anything like that   Are you currently running the sponge. The tank should smell like clean water. Or slightly fishy water. Wondering if it wouldn’t be easier to treat the tank with a round of erythromycin 

[Lonkley]

Are you using tap water dechlorinator? You may have chloramine.

Also you didn't mention ph.

Do any aerosols get used in the room.

What did you set your heater at.

If you're tank is smelling musty you probably have food rotting on the edges or lid 

A lid will only benefit a tank 

Edited March 11 by Lonkley

[Tony s]

On 3/11/2024 at 2:31 PM, Lonkley said:

If you're tank is smelling musty you probably have food rotting

could be, but it could be a general bacterial bloom. possibly blue green algae. pictures would be useful at this point. as well as parameters

[TOtrees]

Your description suggests this has happened multiple times. How many times? Always bettas? How long are the fish surviving? 

[FishRBeautiful]

Here’s a picture. The thing at the top is a carbon filter, same one I use in my 20 gallon that has 13 fish. 
 

Nitrites and Ammonia are 0. Nitrates up to 15 now. 0 chlorine I don’t know what tap dechlorinator or chloramine are. Hardness is 300 like always. Ph like 8.0 as always. Kh 180 like always. That’s all well water results. I do keep driftwood in my 20gallon but it doesn’t show soft water on tests. 
 

Happens a day or two after I buy the fish. I buy my fish at that lfs for 20 gallon and they rarely die. Small minnows survive the longest, like a few weeks or even months. I put thermometer in there for the bettas so it’s 78. I have no light so never had algae.

It’s not musty, more like rotten or dead stuff or stagnant water. It’s a glass lid, so no air getting in the tank.  My 20 gallon has a big hole in the lid for the HOB. Lid is pictured. Does it need a bunch of plastic cut off to let air in?

[johnnyxxl]

On 3/11/2024 at 2:28 PM, Tony s said:

Honestly, it’s the smell that has me concerned the most. Shouldn’t be anything like that   Are you currently running the sponge. The tank should smell like clean water. Or slightly fishy water. Wondering if it wouldn’t be easier to treat the tank with a round of erythromycin 

I was wondering how long has the tank been empty of fish with water that's been stagnant because that's probably what is killing the fish.  Fish want clean water not stagnant.  I would clean the tank and re do the cycle starting over to be sure 

[Tony s]

The sponge filter is running? If it is there should be enough air getting in by that. And there should be enough water flow to keep it from getting stagnant. 

Air stone behind the heater? Even that should provide enough air into the water.

 

[Lonkley]

The lid is not hermetically sealed. Air gets in and out just fine. Especially with a sponge filter literally pumping air in.

[Tony s]

The hardness of the water is perfectly fine. 85% of the US has the same water. So, no big deal. 

What is the thing floating on the right side of the tank?

That’s the carbon filter? Just a big bag of carbon floating?

Edited March 12 by Tony s

[Tony s]

I’m not sure that’s doing anything for you. Carbon filters work by having water flowing through them. Where they can trap fine particles that go through. And they are a bit controversial anyway. Lots of people don’t/ won’t use carbon. I do. But I run mostly hob’s. Several with airstones or sponge filters as well. 

[Tony s]

The thing with bettas, they are designed to live in mostly stagnant mud puddles. Very small pools is where they come from. Especially in the dry season. That’s why they have a labyrinth organ. So even stagnant water shouldn’t be an issue.

[Tony s]

I think the first thing I’d do is to turn the sponge in the center back on . That will provide enough air and water flow to keep it from getting stagnant. Lid or no lid. The second thing is I’d remove the bag of carbon. It’s not doing much for you right now and may be harboring bacteria since there’s no water flow through it. 
 

the decor and gravel should be fine. I have a dark glow fish tank with mostly the same stuff. Only glow in the dark. 
the lack of light is fine. Fish don’t need it. Room light is sufficient for them
 

sorry, still thinking. This tank is fully cycled? It may not be any longer if it was. Inconsistent ammonia at this point. You may need to add some bacteria back when adding fish. 

How are you cleaning this tank. You shouldn’t need to do much more than some gravel siphoning and water changes . 

You say minnows are living for months? In this tank or the 20g?

the rotten smell still bothers me. Really, the only thing I can see, is that bag. The rest really looks fine. I have a 36g that looks mostly like it. Mine came with a hob but I added an air stone as well. Fake plants, fake gravel. Not having any issues with it. 

[FishRBeautiful]

The floating thing is a carbon filter (the kind I use in my 20 gallon) that someone advised I add a few days ago. I probably should have mentioned I have two sponge filters in there (1 I got a few days ago and haven’t had time to hook up yet). The one that’s been running a few months has an air stone inside (like Girl Talks Fish explained to do). 

On 3/12/2024 at 4:46 AM, johnnyxxl said:

I was wondering how long has the tank been empty of fish with water that's been stagnant because that's probably what is killing the fish.  Fish want clean water not stagnant.  I would clean the tank and re do the cycle starting over to be sure 

Your comment makes a lot of sense to me. Here’s what I’m thinking based on what you said. I’ve had the tank running in between fish, sometimes days, a couple times, probably a whole month or two. I don’t always clean it after a fish dies before adding new ones. I also don’t clean the tank as often as my 20 gallon since I keep it low stocked and nitrates are low. I thought I was keeping the cycle alive but maybe I’m just creating stagnant water. Could there be build up bacteria in the surfaces of the tank, rocks, decor etc or even in the water? Would an antibiotic kill it or would I need to take the tank down and bleach that? I’ve never used bleach in a tank so it totally scares me. 
 

And the minnows that survived were in this tank, not my 20 gallon. 

 

 

 

Or could I just do a series of water changes for a while?

[Tony s]

On 3/12/2024 at 8:26 AM, FishRBeautiful said:

And the minnows that survived were in this tank, not my 20 gallon

Okay, well that’s something anyway.

how are you cleaning the tank in between fish? Please describe your process 

On 3/12/2024 at 8:26 AM, FishRBeautiful said:

Could there be build up bacteria in the surfaces of the tank, rocks, decor etc or even in the water

There most definitely is, that’s where your beneficial bacteria live. The ones that bring the tank to life. Speaking of, what type of bacteria are you adding to your tank. What brand do you use 

[FishRBeautiful]

I use a gravel vacuum to change out the water. Because there’s no algae, I never scrub anything or take out plants and wash them. Should I?

That makes sense. So could bad bacteria live on those surfaces also? You can add bacteria to a tank? Why would you do that? I’ve never done that in my 20g. 

[Tony s]

and, really, if the bag doesn’t have water flowing through it, it isn’t doing anything at all. Carbon doesn’t do anything at all by osmosis. It traps particles because it has very fine micro pores. That grab hold of what goes through it. That’s why you pull it when adding medication. It grabs hold of the medicine. Keeping it out of the water. It doesn’t even add a source of carbon to the tank. It’s basically inert. But it could hold a lot of nasty stuff in it without flowering water.
 

I’m wondering if you pull it and smell it what you’ll find. 

[Tlindsey]

On 3/12/2024 at 8:26 AM, FishRBeautiful said:

The floating thing is a carbon filter (the kind I use in my 20 gallon) that someone advised I add a few days ago. I probably should have mentioned I have two sponge filters in there (1 I got a few days ago and haven’t had time to hook up yet). The one that’s been running a few months has an air stone inside (like Girl Talks Fish explained to do). 

Your comment makes a lot of sense to me. Here’s what I’m thinking based on what you said. I’ve had the tank running in between fish, sometimes days, a couple times, probably a whole month or two. I don’t always clean it after a fish dies before adding new ones. I also don’t clean the tank as often as my 20 gallon since I keep it low stocked and nitrates are low. I thought I was keeping the cycle alive but maybe I’m just creating stagnant water. Could there be build up bacteria in the surfaces of the tank, rocks, decor etc or even in the water? Would an antibiotic kill it or would I need to take the tank down and bleach that? I’ve never used bleach in a tank so it totally scares me. 
 

And the minnows that survived were in this tank, not my 20 gallon. 

 

 

 

Or could I just do a series of water changes for a while?

Cleaning a aquarium with part bleach and water is fine but don't use the splash less brand. Just rinse aquarium out allow to dry out completely. You could also fill with water after the cleaning and add dechlorinator. I personally would replace or clean the substrate ornaments and filter if starting over.

[Tony s]

On 3/12/2024 at 9:08 AM, FishRBeautiful said:

You can add bacteria to a tank? Why would you do that? I’ve never done that in my 20g. 

Okay now we’re getting somewhere. Yes, absolutely have to add a source of bacteria. That’s what maintains your nitrogen cycle.

and, unless you’re tearing down a tank, never clean anything by soap, or bleach. That’s an automatic way to kill your cycle.

try this video, then ask more questions 

 

[Tony s]

for

basic info on cycling, this is good

[Tony s]

And I wouldn't worry about not knowing lot of the aquarium stuff. I started with knowing absolutely nothing. had to learn everything by myself. mostly on websites, then found youtube. never had a use for youtube until then. but seeing things done is easier than having to do things yourself. and you're here. so that's way ahead of where i was.

Ask question, lots of very smart people here who like to help