Help Aquarium Is Starting To Smell, But Parameters Are Good. Please Help!

Señor Pescado

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I have a lightly stocked, 20g (tall) aquarium that has been established for one year. Lately the water has started to smell, and I can't figure out why. The parameters are as follows:

pH: 8.0
Ammonia: 0ppm
Nitrite: 0ppm
Nitrate: 10-20ppm

The aquarium is stocked with one dwarf gourami, eight neon tetras and two amano shrimp. It's not always easy to find both amanos, and currently I can only account for one. However, while vacuuming the gravel, I'm always sure to vigorously swirl the gravel vac around, just above the sand substrate; if one was dead and behind some aquarium decor, I think it would have floated out by now.

I'd appreciate any and all input as to what could be causing this.

Thank you.
 
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Señor Pescado

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What does it smell like?
It's got a 'dirty pond' smell to it. That's the best I can come up with. It is certainly not a sulfur-like scent.
Add some activated carbon in your filter.
I was considering this. I currently don't use any carbon in my filter. Would this be a band-aid to a bigger problem, or do you think it's just normal for an aquarium to smell after a while if there's no carbon present?
 

Crispii

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I don't think that it's normal for aquariums to smell since I never smell any odors coming from my tanks before.
 

pagoda

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My aquariums sometimes whiff of onions....not sure why onions exactly but they do...anyway its usually when the Fluval carbon filled fake moss balls are due to be replaced (they last a max of 2 months before they need to be thrown away & replaced) and the carbon in the filter needs to be changed. Once done, everything smells of warm water again
 

kallililly1973

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Also check for food on the inside of your rim and around your light and lid to rule out the possibility of decaying foods being the odor. Add the carbon for a week and see if it goes away then take it out and see if the smell returns. Could also be some build up in your filter. When was the last time it was cleaned?
 

PascalKrypt

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Actually planted and/or well-stocked tanks have an odor (just normally not a strong one), I thinking smelling your tank to identify problems is underrated. No, I'm being serious. It actually works. Problem is that it can be a little hard to explain what smells are like...

What you are describing sounds like organic decay of some sort. If you have live plants, are all of them doing well? Have you checked inside your filter to see if there is anything stuck in there? Any floating plants or other debris stuck between your heater/filter cables and the glass, the rim of your lid?

If it is more of a fishy smell (like the pungent smell of a fish vendor on a warm day) that would signal something else though.

And yes, if it takes some kind of special filtration to go away I would be worried about the state of things in your tank because most likely something is off that should be fixed.
 

aae0130

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a freshwater aquarium without carbon can get a little bit “earthy” smelling but nothing that would emminate in the room. As long as you are not smelling it in the room that contains the aquarium then I wouldn’t fret.
 

Noroomforshoe

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You said you hover over the gravel with the Vacuum? Is that true? do you only hover over the gravel? you must stir up the gravel everytime gently with the gravel vacuum. Sorry if I read wrong.
yes carbon removing a smell is a band aid not a fix unless you are super sensative to the normal wet earth sort of smell of aquariums. Please be sure that you are testing properly as both liquid and paper tests go bad. it would be a good idea to take some water to a petstore and see if results match up.
 

DoraCory

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All of my aquariums have an earthy pond kind of smell, but you really have to lean over the water and actually sniff it to smell that.
 

BGK Unlimited

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It's got a 'dirty pond' smell to it. That's the best I can come up with. It is certainly not a sulfur-like scent.

I was considering this. I currently don't use any carbon in my filter. Would this be a band-aid to a bigger problem, or do you think it's just normal for an aquarium to smell after a while if there's no carbon present?
I do believe so that it really takes a while for the aquarium to smell and after a few days or weeks it will wear off eventually
 
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Señor Pescado

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Also check for food on the inside of your rim and around your light and lid to rule out the possibility of decaying foods being the odor. Add the carbon for a week and see if it goes away then take it out and see if the smell returns. Could also be some build up in your filter. When was the last time it was cleaned?
I hadn't checked the rim for decay/food; thanks for the tip! However, none there. I just cleaned the filter about ten days ago.

Actually planted and/or well-stocked tanks have an odor (just normally not a strong one), I thinking smelling your tank to identify problems is underrated. No, I'm being serious. It actually works. Problem is that it can be a little hard to explain what smells are like...

What you are describing sounds like organic decay of some sort. If you have live plants, are all of them doing well? Have you checked inside your filter to see if there is anything stuck in there? Any floating plants or other debris stuck between your heater/filter cables and the glass, the rim of your lid?

If it is more of a fishy smell (like the pungent smell of a fish vendor on a warm day) that would signal something else though.

And yes, if it takes some kind of special filtration to go away I would be worried about the state of things in your tank because most likely something is off that should be fixed.
I don't currently have live plants. I did check around the rim of the tank, and I can't find anything stuck or decaying. It doesn't smell fishy. It smells like what I'd imagine a dirty aquarium smells like.

You said you hover over the gravel with the Vacuum? Is that true? do you only hover over the gravel? you must stir up the gravel everytime gently with the gravel vacuum. Sorry if I read wrong.
yes carbon removing a smell is a band aid not a fix unless you are super sensative to the normal wet earth sort of smell of aquariums. Please be sure that you are testing properly as both liquid and paper tests go bad. it would be a good idea to take some water to a petstore and see if results match up.
No, you read that right. I have about an inch of sand substrate. Every other water change, I'll stick the gravel vac down into the sand to clean & stir it up. The other times, I just swirl it right above the surface so the detritus lifts up and I vac it all out. The morning everyone was complaining of 'the smell' was after the first day in a while that we didn't run our forced air system in the house. Without the air circulation, maybe we were all just sensitive to the smell.

I find algae even in small amounts causes a smell, particularly when exposed to air during a water change.

Any algae in the tank?
I was wondering about algae. I get a slow growth of normal, green algae that will show up on the glass and aquarium decor over time. The amanos keep it pretty clean though.
 

PascalKrypt

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The only green growth that would smell really putrid is cyanobacteria, but that is more sulphur-like (as in what you described it wasn't). Another option is anoxic reactions in your substrate, as aquarium sand is relatively dense and under certain circumstances may compact to create those conditions. If those pockets of gas produced are released during or after a vacuuming session, that could cause the bad smell but I wouldn't expect it to last for days in that case.
Sometimes fish that are dying or suffering from severe bacterial infections can excrete a very strong smell, but it is a recognisable one and I'm not sure if I would describe it as "what you expect a dirty aquarium to smell like". That's why it is hard to talk about recognising scents over the internet. Anyway, it might be a good idea to check your fish for signs of ill health if you really can't find anything decomposing in your aquarium.

Do you have hardscape in there, especially any wood or other organic materials? Did the start of the smell coincidence with anything being added to, removed from or changed in your tank? What does the colour of your water look like?
How often do you do water changes and how much do you change out, btw?
 
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Señor Pescado

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Do you have hardscape in there, especially any wood or other organic materials? Did the start of the smell coincidence with anything being added to, removed from or changed in your tank? What does the colour of your water look like?
How often do you do water changes and how much do you change out, btw?
All decor is resin/synthetic. No changes to tank, stock, decor, etc. Water is crystal clear. I change 30% every seven to ten days; nitrate cycles between 10 to 20 ppm during this time. No signs of stress in fish. From the reports I'm getting, the tank didn't smell today. Maybe the cause was temporary.
 

kallililly1973

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All decor is resin/synthetic. No changes to tank, stock, decor, etc. Water is crystal clear. I change 30% every seven to ten days; nitrate cycles between 10 to 20 ppm during this time. No signs of stress in fish. From the reports I'm getting, the tank didn't smell today. Maybe the cause was temporary.
Also i think you mentioned if im in the right thread that you trimmed some decaying or not so healthy plant leaves so that could also have had some impact on the odor. Hope it clears up for you and your paramaters are all good and it goes away on its own. Could have been the tap water and/or water conditioner causing an odor as well. I know when i use Prime when i open the bottle i can smell a bit of a "stench" but once the tank is filled back up its like a ray of sunshine over a pond
 
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