# This ones complicated... Sulfur Smell, but not Hydrogen Sulfide?



## kmacF30

I have two tanks a 20 and a 29 gallon which have been set up for about 7 months. About a week and a half ago, out of nowhere, my 20 gallon tank began to stink. It was like a rotten egg odor that filled up the entire house. Desperate to get rid of it I did an gigantic water change and gravel vac (About 80%). The smell got very mild, until the next morning it was horrific again. I checked my parameters: Ammonia 0, Nitrate 5 ish, Nitrite 0, Hardness 75, Chlorine 0, Alkalinity 80, PH 6.5 ish. Everything was where it generally is although nitrate was significantly lower than normal since I had done such a big water change. So I started doing some research on rotten egg smell in freshwater aquariums and everything pointed to hydrogen sulfide. However I was somewhat perplexed however, since at the impact of the odor was so strong and there seemed to be absolutely no effect on my fish. At this point I was in such of a panic I went drastic: I threw out all of my live plants, put the fish in a tub of new de-chlorinated water, drained my entire tank, twrew out all gravel, soaked decorations in hot water, bought new gravel, scrubbed the tank with hot water, Threw out all filter media (ran hot water through the filter) and essentially started over. I essentially destroyed my cycle, but eliminated all possibilities of hydrogen Sulfide in my tank. 

Things went well for the next couple of days, the fish were coping well, I added Biospira and had been helping the fish cope with elevated nitrites using Seachem prime. The next day out of nowhere just like my 20 gallon tank, My 29 gallon tank began to emit the same foul odor. I followed the same exact drastic measures as I did with the other tank since I thought I had had success previously. About 7 days passed after I eradicated the odor in the 29 gallon, all off the fish were doing good (Zero fish loss!) when all of a sudden, last night, the odor came back in my 20 gallon. I was completely floored.... ! Being in my bedroom I was desperate to get some sleep, so I did another huge water change (about 80%). Since then the odor has subdued, the fish are not showing any signs of stress, However I decided to contact my LFS which I should have done in the first place She told me that the chance of having hydrogen sulfide in both tanks all of a sudden was highly unlikely and asked if I had any algae blooms recently. As I thought about it I have noticed some patches of light/dark green algae almost looking like mold spores growing on the side of the glass in both tanks. She told me that was exactly what I was smelling and that high phosphates were the main cause of it. She said it could be blue/green algae which can very difficult to get rid of. (I do have UV Sterilizers in both tanks BTW). She told me that even the smallest amount that was not killed when I drained my tanks could regrow and start to smell again. I will be bringing down some water samples to test phosphate levels, but in the mean time I bought some Fluval Clearmax inserts for my 70 gallon and 50 gallon Hang-on filters. These inserts claim to reduce phosphate dramatically. 

As of right now my 29 gallon has no smell at all and my 20 gallon has a very faint smell only if i put my nose up to it. Is there really such an algae that can produce such a noxious smell that I experienced? Or is there some possibility that there is hydrogen sulfide in my tanks? Sorry for the long thread. I am just exhausted by this and am searching or answers. I am super paranoid this will come back again.


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## corina savin

Sulfur does not smell, Hydrogen sulfide does.
I don't believe it is an algae issue. Further, high phoshates level causing algae is a controversial idea, IME there is no connection.
I will consider a bacteria imbalance as a main cause.
Hydrogen sulfide is readily formed in the substrate (from sulfates in the water or proteins in the fish food, assuming the substrate itself does not leach sulfates)
Sulfate-reducing bacteria are associated with severely anaerobic conditions.
Hydrogen sulfide destruction require oxygen to convert H2S to (SO4)2-, but it can be carried out anaerobically as well in the presence of light (D Walstad, Ecology of the Planted Aquarium, pg 67-68)


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## kmacF30

corina savin said:


> Sulfur does not smell, Hydrogen sulfide does.
> I don't believe it is an algae issue. Further, high phoshates level causing algae is a controversial idea, IME there is no connection.
> I will consider a bacteria imbalance as a main cause.
> Hydrogen sulfide is readily formed in the substrate (from sulfates in the water or proteins in the fish food, assuming the substrate itself does not leach sulfates)
> Sulfate-reducing bacteria are associated with severely anaerobic conditions.
> Hydrogen sulfide destruction require oxygen to convert H2S to (SO4)2-, but it can be carried out anaerobically as well in the presence of light (D Walstad, Ecology of the Planted Aquarium, pg 67-68)


So theoretically multiple airstones and light would solve a hydrogen sulfide problem? Is it a long process? Because I am running 3 airstones with two pumps, along with a very bright Fluval LED light. I also have been stirring up the gravel to look for bubbles or an increase in smell and have not found any correlation... It one point I even lowered the water level to increase aeration. As for my substrate it is gravel (about an inch and a half deep)... could there still be pockets of H2S in shallow gravel?

As for the smell, today its a little stronger, its still only if i'm close to the tank. I have also wondered if the prime is causing the milder smell, but have ruled that out since I am using the same dose in my 29g and the water has no smell at all.


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## corina savin

Yes, airstone is what I would try first. It helps in many ways: adding oxygen, drive H2S out, increase water movement at the substrate level, increase air movement at the water surface. 
Next step, I will consider Hydrogen peroxide (or Potassium permanganate) as an oxidant.
Iron will be able to precipitate H2S, making the black, ugly FeS.
Interesting topic. Keep me posted


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## Kim

Did the water turn cloudy at all? I agree with the bacteria hypothesis (which also explains the transfer between the two tanks), and had a similar experience with a 10 gallon tank with gravel substrate several years ago. The water turned cloudy and smelled terribly like rotten eggs over the course of one day, and after some research I was able to identify this as a bacterial bloom. I ended up sticking in several airstones and performing large (around 75%) water changes daily. In a few days the smell was gone and the water was clear again. All of the fish were fine, and afterward everything went right back to normal. Hopefully the same will occur for you.


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## beaslbob

kmacF30 said:


> I have two tanks a 20 and a 29 gallon which have been set up for about 7 months. About a week and a half ago, out of nowhere, my 20 gallon tank began to stink. It was like a rotten egg odor that filled up the entire house. Desperate to get rid of it I did an gigantic water change and gravel vac (About 80%). The smell got very mild, until the next morning it was horrific again. I checked my parameters: Ammonia 0, Nitrate 5 ish, Nitrite 0, Hardness 75, Chlorine 0, Alkalinity 80, PH 6.5 ish. Everything was where it generally is although nitrate was significantly lower than normal since I had done such a big water change. So I started doing some research on rotten egg smell in freshwater aquariums and everything pointed to hydrogen sulfide. However I was somewhat perplexed however, since at the impact of the odor was so strong and there seemed to be absolutely no effect on my fish. At this point I was in such of a panic I went drastic: I threw out all of my live plants, put the fish in a tub of new de-chlorinated water, drained my entire tank, twrew out all gravel, soaked decorations in hot water, bought new gravel, scrubbed the tank with hot water, Threw out all filter media (ran hot water through the filter) and essentially started over. I essentially destroyed my cycle, but eliminated all possibilities of hydrogen Sulfide in my tank.
> 
> Things went well for the next couple of days, the fish were coping well, I added Biospira and had been helping the fish cope with* elevated nitrites using Seachem prime*. The next day out of nowhere just like my 20 gallon tank, My 29 gallon tank began to emit the same foul odor. I followed the same exact drastic measures as I did with the other tank since I thought I had had success previously. About 7 days passed after I eradicated the odor in the 29 gallon, all off the fish were doing good (Zero fish loss!) when all of a sudden, last night, the odor came back in my 20 gallon. I was completely floored.... ! Being in my bedroom I was desperate to get some sleep, so I did another huge water change (about 80%). Since then the odor has subdued, the fish are not showing any signs of stress, However I decided to contact my LFS which I should have done in the first place She told me that the chance of having hydrogen sulfide in both tanks all of a sudden was highly unlikely and asked if I had any algae blooms recently. As I thought about it I have noticed some patches of light/dark green algae almost looking like mold spores growing on the side of the glass in both tanks. She told me that was exactly what I was smelling and that high phosphates were the main cause of it. She said it could be blue/green algae which can very difficult to get rid of. (I do have UV Sterilizers in both tanks BTW). She told me that even the smallest amount that was not killed when I drained my tanks could regrow and start to smell again. I will be bringing down some water samples to test phosphate levels, but in the mean time I bought some Fluval Clearmax inserts for my 70 gallon and 50 gallon Hang-on filters. These inserts claim to reduce phosphate dramatically.
> 
> As of right now my 29 gallon has no smell at all and my 20 gallon has a very faint smell only if i put my nose up to it. Is there really such an algae that can produce such a noxious smell that I experienced? Or is there some possibility that there is hydrogen sulfide in my tanks? Sorry for the long thread. I am just exhausted by this and am searching or answers. I am super paranoid this will come back again.


that's where the smell is coming from.

my .02


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## kmacF30

Kim said:


> Did the water turn cloudy at all? I agree with the bacteria hypothesis (which also explains the transfer between the two tanks), and had a similar experience with a 10 gallon tank with gravel substrate several years ago. The water turned cloudy and smelled terribly like rotten eggs over the course of one day, and after some research I was able to identify this as a bacterial bloom. I ended up sticking in several airstones and performing large (around 75%) water changes daily. In a few days the smell was gone and the water was clear again. All of the fish were fine, and afterward everything went right back to normal. Hopefully the same will occur for you.


The water never turned cloudy, but I a very happy to report that its been a few more days since this post and my 29 gallon tank has no traces of the smell at all now.  The tank is also almost on its way to being fully cycled again.

As for the 20 gallon unfortunately this tank gave off a strong odor yesterday morning. After trying the large water changes for several days now and running several airstones, I decided to strip the tank down one more time. This time though, I was much more thorough hopefully annihilating any possibility of the bacteria or the smell returning. Interestingly enough, after i removed the fish this time, I decided to stir the gravel. This time I did have some pockets of air escape, however , the smell didn't seem to get too much stronger.

Anyway, I took this cleaning 10 steps further, by soaking the tank, gravel and decorations all in scolding hot water and vinegar. I bought an entirely new filter (marineland HOB), new heater, new airstones, and sanitized everything else possible. (Unfortunately this will mean completely re-cycling again). I also wanted to eliminate the chance of Hydrogen sulfide by lowering the gravel even more from 1-1/2 inches to just an inch for now. As for some of the flat bottom decorations, I drilled multiple holes in each of them allowing oxygenated water to pass through. So as of now its a waiting game. so far the fish are doing good. There is the mildest odor this morning but i'm not going to draw any conclusions right now because the other tank had a mild odor for a few days, then it went away. Hopefully this will do it  Thanks for the help so far everyone!


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## kmacF30

beaslbob said:


> that's where the smell is coming from.
> 
> my .02


It funny because I have considered that. but have never had an issue before... I have been using way less though.


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## kmacF30

Okay well I wanted to keep you guys up to date. Its been bout a week now and the smell is gone from both aquariums  I'm not sure what it was nor do I think I will ever be sure. All I know is it seemed like following the strip down of both tanks, the smell continued. I then switched from Fluval to Marineland filters, upgrading from a 50 and a 20 to one 70 on the 29 Gallon and swapping out the 50 Fluval to a 50 marineland on the 20 gallon. I have to say, I like the marineland filters better. They're feel less flimsy, there is much more water flow so the media isn't jammed in and you can put up to 4 cartridges in the 70 gallon one! I also still use some of the fluval media like the Ammonia remover since my tanks are overstocked.

This brings me to the next thing I did which was to test for Phosphates per the LFS's recommendation. The tank which did not smell was a .5, while the tank which stunk was a 2.5. My tap water was a 0. So having not to many other options I put in some phosphate removing media by seachem in both filters. I took about 5 days and the smell dissipated. REALLY WEIRD Does anyone have any explanation for this? Should I take this course of action if the smell comes back? Is there any connection between phosphates and what I could have experienced? Thanks for all the help everyone!

I'm going to give it about 3 more weeks and if I don't have any more problems I am going to upgrade the 29 gallon to a beautiful 56 Gallon Bow-front aquarium, and the I'm going to put all of the fish in my 20 into the 29. It needs to happen soon, because the new Featherfin Catfish I got is gonna need the space. Hes been sparring a little with my blood parrot.

LOL there should be an addiction forum on this website! I cant stop buying fish!


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## corina savin

All I can think of is that you are over-feeding.
I know the best part to watch your fish is at feeding time. That's the only interaction we have with our pet fish (since we cannot pet or cuddle them).
Even if fish is eating all the food available, the more they eat, the more waste they produce.
Pellets are better than flakes in maintaining water quality. Live and frozen food- the worst.
I feed my fish frozen blood worms once a week, the day before the water change. I try not to feed for a day or two, especially after I service the canister filter.


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## Flear

have not red except for a few points.

if you are stiring up the substrate looking for bubbles,...
-those bubbles could be CO2
-if your substrate is deep it could be N2 or H2S
-(could be others)

but if it's H2S, ... quit stirring up the substrate, you are going to cause your tank all kinds of misery (dead fish)

the stuff at the bottom of the substrate needs remain at the bottom, ... doing stuff to mix that with the rest of the tank, ... toxic disolved gasses will move slowly on their own, slow enough things are safe. if you are mixing things up you are putting these toxins directly into the water column.

the stuff at the top doesn't matter, this is safe, ... it's the stuff at the bottom that will kill your tank

---

H2S does have a tell-tale blackness about it - it stains the gravel/rocks/sand black
low levels of H2S you can smell
high levels you cannot (and are just as toxic to you)

this does need your substrate to be deep enough/fine enough to ensure there is no dissolved oxygen in the bottom layers (bacteria use it up)

---

will have to read through this later (after work) for more information to see if i've been talking garbage (not related) or not


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## Flear

having red everything fully this time.

i would likewise rule out anything from anoxic substrate
if it's cyano, ... i only have bits i have red & stumbled across and theory ...
water flow, ensure plenty of water flow.

the air-stones ...
in my tank i've got all the airstones on the short wall (well it's one long single airstone)
this creates a drag of water from the bottom, up the side, and across the top, ... plenty of gas exchange (CO2, O2, N2, etc) the water heading towards the side is going to be dragging along the bottom, ensuring fresh water at the bottom of the tank
-well that's it for theory for dealing with cyano, i've never had it so i can't say otherwise.

---

from other comments, i would change how much you are feeding them and/or change the brand of food.

phosphates are a so-called 'natural' preservative, cheap, and adds weight, ... win-win-win for the manufacturer, sucks for the buyer.

as you know your tanks are over-crowded, so that may make it harder to limit feeding.

i was going to suggest get some snails for the excess food, ... but this won't change anything, food goes in, poop comes out, ... still have lots of whatever is causing the problem.

---

a UV sterilizer, personally i wouldn't get one of these, ... because i'm weird and i want plankton in the water, ... anyway, ...

one article i came across mentioned "do not get cheap ones" (close enough), water flow vs UV bulb means it's not doing much (i don't recall why, but i think mentioned about either the bulb may not be strong enough, or the water flow is too fast for the bulb so it can't do it's job.

complete article (i actually like this site for info 
Aquarium & Pond UV Sterilization | How to use a UVC Sterilizer

---

other ideas, ... plants

no plants are not the magic cure-all they are often made out to be, ... but they can make aquarium life so much simpler for everyone.

namely, they'll make use of whatever nutrients are building up in the water, at first everyone will complain about algae (in your case this mysterious stinky sulfer/rotten egg smelling bacteria) as the plants grow and develop, populate the tank, GET HEALTHY, ... they will outcompete undesireable stuff for nutrients to stay alive, ... 

from one site well known Tom Barr mentioned that being focused on the algae is the wrong way to go about things, ... i agree, ... focus on your plant health, ... another thing mentioned in regards to so many people being impatient about wanting instant fixes ASAP for their algae problems, ... give it a year from the plants to really establish themselves and it seems algae problems then dissapear

-or in your case this stinky bacteria.

oh ya, with plants, ... don't vacuum the substrate, the roots like access to the nutrients that are breaking down in it.

---

that's it for me for ideas
doesn't mean i'm right, and we'll never know unless you make one change and suddenly everything clears up

another source, ... if the bacteria is floating in the water, ... fun idea, but your fish would eat them too quickly, ... zooplankton (rotifers, daphinia & such) will eat such stuff living in the water, ... 

other crazy ideas, clams & sponges will do the same as well, ... but these are considerably more tricky.
clams are great if they do their job, ... but if they are not getting enough to eat starvation could take months
sponges, ... want silica - so does diatoms, ... so having one healthy means you have a great environment for the other :/

---

yay, we're in the advanced room 
i get scolded if i say so much in the beginner room 

Edit:
for cleaning, ... if going this route alone ...

a massive cleaning will cause a die-off of bacteria in the tank - because they can't get enough food stuffs (nutrients) to survive
not all, but enough
this in turn becomes detritus and in turn nutrients that will feed the next generation of the same bacteria that survived
doesn't mean you can do much as you can't remove so much nutrients to kill everything, ... and you wouldn't want to or you will risk crashing the nitrogen cycle bacteria you have going.

just an odd note for curiosities sake 
get to see/understand a little more about what goes on that isn't talked about

as i found from experience, this can also do some major hurt to algae (i was growing it intentionally as an extra treat for flagfish in the tank - growing it in one of those fry cage things so the fish couldn't eat it all on their own)


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## kmacF30

Flear said:


> having red everything fully this time.
> 
> i would likewise rule out anything from anoxic substrate
> if it's cyano, ... i only have bits i have red & stumbled across and theory ...
> water flow, ensure plenty of water flow.
> 
> the air-stones ...
> in my tank i've got all the airstones on the short wall (well it's one long single airstone)
> this creates a drag of water from the bottom, up the side, and across the top, ... plenty of gas exchange (CO2, O2, N2, etc) the water heading towards the side is going to be dragging along the bottom, ensuring fresh water at the bottom of the tank
> -well that's it for theory for dealing with cyano, i've never had it so i can't say otherwise.
> 
> ---
> 
> from other comments, i would change how much you are feeding them and/or change the brand of food.
> 
> phosphates are a so-called 'natural' preservative, cheap, and adds weight, ... win-win-win for the manufacturer, sucks for the buyer.
> 
> as you know your tanks are over-crowded, so that may make it harder to limit feeding.
> 
> i was going to suggest get some snails for the excess food, ... but this won't change anything, food goes in, poop comes out, ... still have lots of whatever is causing the problem.
> 
> ---
> 
> a UV sterilizer, personally i wouldn't get one of these, ... because i'm weird and i want plankton in the water, ... anyway, ...
> 
> one article i came across mentioned "do not get cheap ones" (close enough), water flow vs UV bulb means it's not doing much (i don't recall why, but i think mentioned about either the bulb may not be strong enough, or the water flow is too fast for the bulb so it can't do it's job.
> 
> complete article (i actually like this site for info
> Aquarium & Pond UV Sterilization | How to use a UVC Sterilizer
> 
> ---
> 
> other ideas, ... plants
> 
> no plants are not the magic cure-all they are often made out to be, ... but they can make aquarium life so much simpler for everyone.
> 
> namely, they'll make use of whatever nutrients are building up in the water, at first everyone will complain about algae (in your case this mysterious stinky sulfer/rotten egg smelling bacteria) as the plants grow and develop, populate the tank, GET HEALTHY, ... they will outcompete undesireable stuff for nutrients to stay alive, ...
> 
> from one site well known Tom Barr mentioned that being focused on the algae is the wrong way to go about things, ... i agree, ... focus on your plant health, ... another thing mentioned in regards to so many people being impatient about wanting instant fixes ASAP for their algae problems, ... give it a year from the plants to really establish themselves and it seems algae problems then dissapear
> 
> -or in your case this stinky bacteria.
> 
> oh ya, with plants, ... don't vacuum the substrate, the roots like access to the nutrients that are breaking down in it.
> 
> ---
> 
> that's it for me for ideas
> doesn't mean i'm right, and we'll never know unless you make one change and suddenly everything clears up
> 
> another source, ... if the bacteria is floating in the water, ... fun idea, but your fish would eat them too quickly, ... zooplankton (rotifers, daphinia & such) will eat such stuff living in the water, ...
> 
> other crazy ideas, clams & sponges will do the same as well, ... but these are considerably more tricky.
> clams are great if they do their job, ... but if they are not getting enough to eat starvation could take months
> sponges, ... want silica - so does diatoms, ... so having one healthy means you have a great environment for the other :/
> 
> ---
> 
> yay, we're in the advanced room
> i get scolded if i say so much in the beginner room
> 
> Edit:
> for cleaning, ... if going this route alone ...
> 
> a massive cleaning will cause a die-off of bacteria in the tank - because they can't get enough food stuffs (nutrients) to survive
> not all, but enough
> this in turn becomes detritus and in turn nutrients that will feed the next generation of the same bacteria that survived
> doesn't mean you can do much as you can't remove so much nutrients to kill everything, ... and you wouldn't want to or you will risk crashing the nitrogen cycle bacteria you have going.
> 
> just an odd note for curiosities sake
> get to see/understand a little more about what goes on that isn't talked about
> 
> as i found from experience, this can also do some major hurt to algae (i was growing it intentionally as an extra treat for flagfish in the tank - growing it in one of those fry cage things so the fish couldn't eat it all on their own)


Hi, I really appreciate your feedback! Well it has been several weeks since the smell has gone away. I agree with you though, whatever it was It must have been some type of bacteria. It probably was a mistake to completely strip down the tanks as i did because as you said, it kills the nitrogen cycle and considering the smell returned after doing so, Your theory about it being nearly impossible to kill off all bacteria was most likely the case.

I think when I had plants in my tank, i did make the mistake of gravel vacuuming too deep near the roots, as i suspected that before I stripped down the tanks, some of the plants may have begun to rot. I happy to report however that despite hurting the nitrogen cycle in both tanks, I have managed to get both tanks completely cycled again with zero fish loss  

Whatever this may have been there seemed to be some correlation between adding the phosphate remover to my filters and the smell dissipating. I don't know if the excess phosphate I had served as a nutrient to the possible bacteria which my have caused the smell...? I am also wondering if I should continue to use the phosphate remover..... 

As for my UV sterilizers, I will check out that article... All i know is it seems I have had very good luck with them. A few times I may have accidentally introduced some fish from the LFS that have had minor ich and interestingly enough, not only did the ich not spread to the other fish, but it would clear up very quickly using the heat method.

Aside from all of this I have my eye on a beautiful 56 gallon Bow-front glass tank that I plan on getting in about a week. Can't wait, and I just hope everything goes smoothly! If anyone has any good advice on tank upgrades that can help minimize the stress on fish, any advice is much appreciated 

Thanks again for the help!


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## Flear

the aquaclear foam filter blocks, ... i love those things 

load them into the tank, let them populate for nitrogen cycle, ... when you get your new tank, they're ready to assist you


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