My fish tank smells like onions

Michelina Miedema

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I have a 6 by 12 inch tank ( I believe 2.5 gallons) and it smells horrible. The smell is extremely strong and distinctly smells like onions!!!!

I have tested pretty much everything individually in the tank, the marbles, the plants, the food, the water and the decorations and have come to the conclusion the fish have to be the source of the smell? I have built this double tank for my two betas to live, they both seem happy and healthy (both build bubble nests and eat normal amounts about 4 pellets a day). I have an exact replica tank that I built with my other two fish that I've had for a year and never had a problem with odor in their tank.
I feed all 4 betas the same food so that can't be the problem either.

I even returned the tank to petco and bought a new one thinking the smell came from the sealant on the tank but the smell returned within 4 days strong as ever! I have no idea what the problem could be.

could anyone recommend a water treatment maybe? I'm changing 50 percent of their water every few days at this point and my other tank I change once a month just to remove waste, the have no smell!
ANY suggestions will help!!!! I'm feeling hopeless IMG_5228.jpgIMG_5229.jpgScreen Shot 2014-08-11 at 10.43.20 PM.pngScreen Shot 2014-08-11 at 10.43.36 PM.pngIMG_5228.jpgIMG_5229.jpgScreen Shot 2014-08-11 at 10.43.20 PM.pngScreen Shot 2014-08-11 at 10.43.36 PM.png
 

junebug

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It won't.

Something in the tank must be causing the issue. What exactly is in this tank? Any live plants? Any oddball decorations? Is there biofilm on the top of the water?
 

Aquarist

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Good morning,

Activated Carbon:
My two cents on activated carbon: I'm a firm believer that every freshwater aquarium should use it. Granted it is a personal choice and many members only use it at certain times, if they use it all. I respect that and it's their decision.

I use it around the clock in all of my tanks, changing it out every 3 weeks. I don't feel that carbon masks any problems but removes them as long as you change it out periodically. I change mine every 3 weeks for fresh. It absorbs minerals and organic substances, helps to keep your water clear, eliminates foul odors. It will also remove medications and discoloration in the water (caused by driftwood for an example). If you're running more than 1 filter on a tank, the carbon does not have to go into every filter only 1. The other filters you can stuff full of good bio media. (sponges, ceramic cubes and tubes, bio balls).

I've stopped saying that the Activated Carbon (AC) leaches what it has collected back into the tank. There are people on both sides of the fence here. Instead I think it's more accurate to say the the AC looses it effectiveness after 3 to 4 weeks and it should be removed and replaced.

It has been my experience that Activated Carbon will not remove a bacterial bloom.


If your tank smells foul then I highly recommend adding it to your filter immediately. A water change would probably be a good idea too.

Activated Carbon

Ken
animal0028.gif


My tanks are crystal clear!
happy0064.gif
 

cichlidman

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I see no filters or water movement my guess it is getting stagnate or some bacteria
 

bowen747x

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wait you don't run a filter? woah!? I also see your water isn't filled to the top, and you say you usually only change the water once a month? what about nitrates? do you test your water? I'm so confused

I don't know how you can have smelly water if your putting fresh water in a new tank, maybe you need to cycle tho? I think we need more info
 

ryanr

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HI Michelina, welcome to Fishlore

Can you give us a little more information about the setup?

You mentioned you have other tanks, what are the differences between the ones that don't smell and this one? Filter, lighting, feeding etc.

I can't say I've ever experienced an 'onion' smell, but if you mean it smells a little like ammonia, then my guess is the tank is cycling. For more info on the Nitrogen Cycle: https://www.fishlore.com/NitrogenCycle.htm

An interesting observation above about filters and water movement. It is possible the issue is related to a lack of filtration/water movement.

Whilst you get on top of things, if you can get a bottle of Seachem Prime water conditioner, it may help, as it detoxifies ammonia in the water.

Also - how is your betta looking? The health of the fish can help determine what type of issue you might be experiencing.

And lastly, Ken's advice on carbon is sound. But to start, let's try figure out what's going on.....
 

Anders247

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If you do use activated carbon make sure it is phosphate-free, as too much phosphates will cause thread and slime algae to grow.
 

Dolfan

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I agree you need a filter. Otherwise they are just sitting in a giant pool of their own waste. The filter will help filter out the waste and get rid of the smell.
 
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Michelina Miedema

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I have no filter at all but neither does my other tank that I've had for almost a year and that one has absolutely no smell or anything!I have two different types of live plants one on each side. and the decorations are nothing out of the ordinary. it just seems strange to me

and it really smells exactly like onions not like ammonia or anything else its so bizarre! I certainly can purchase a filter or that conditioner you mentioned. my fish look and act very healthy! they move around a lot and eat and make bubble nests all the time. its such strange situation I'm so sad for them
 

Dolfan

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Unless you do daily water changes, both tanks need filters. Bacteria is weird stuff, certain "onion smelling" bacteria could be in one tank but not the other. It could also have to 2 with having 2 fish, so twice as much waste. Once bacteria, mold, or whatever funky substance gets a foot hold on your tank it will be hard to get rid of without a 100% water change and full tank breakdown/cleaning.

You could easily get a sponge filter that would help in both tanks. One air pump could run both filters and you could get some of the cheap sponge filters from ebay that are around $4 each including shipping. $10-15 for an air pump, $2 for some tubing and you are good to go, and your fish will be much better off. The movement of the water will help prevent it stagnating.
 
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Michelina Miedema

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I wash and clean everything in the tank often since the smell is so strong . I don't use a filter on this tank or my other one, but the other one has never had a problem with smell!

yeah I think I'm going to try out a sponge filter today. I do 100 percet water changes once in a while too and the same smell always returns :/. hopefully a filter will help
 

bowen747x

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I'm a noobie around here but I think you also need to cycle your tanks? do you know what your ammonia, nitrite and nitrate readings are? or your ph? that stuffs pretty important
 

Maverick

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Could it be the food...? Or maybe one of the plants is some kind of water-onion?

Hope the filter solves it! It's always good to have one those set up. I have a betta as well and run the filter once every 2-3 days for a few hours.

Best of luck!
 

junebug

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My guess is a bacteria growing back due to lack of water movement. Anaerobic bacteria is nasty stuff.
 

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