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How should a tank smell?


Chad
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I'm trying to track down a stressor/problem in my aquarium and I could use some insight regarding the smell of a tank. My tank smells earthy, like dirt, most of the time. I believe that's good, planted tank (20 gal long, floating, mosses and ferns), populated with 15 guppies, a bristle pleco, 15 shrimp and 4 mystery snails. But when I clean it, specifically gravel vac it, it smells like sulphur (rotten eggs). Is that an indicator of something bad? Seems like it would be. Are more water changes the answer? My levels are all good I think (amm 0%, nitrite 0%, nitrate 10%, ph 7.4, kh 5, gh 9) except for phosphate which comes out of the tap at 1.0 ppm and is currently 3-4 ppm in my tank. Don't know what I should be looking for but generally the fish have clamped fins except for a couple of them. I worry I overfeed them but it's not excessive, meaning there isn't food in the tank after five minutes, but I have dealt with swollen bladder issues in the past so I'm working on it and still trying to find the perfect amount. Any insights are hugely appreciated, thanks so much!

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If it smells like rotten eggs, it's probably Hydrogen Sulfide. Hydrogen Sulfide occurs when there is decomposing organic matter (fish food, dead plants, waste, etc.) Usually, anaerobic bacteria is the culprit. It occurs when there isn't enough flow. Since there isn't enough flow, and or, oxygen, it might be the anaerobic bacteria taking over, and using the fish waste, as the Hydrogen Sulfide is one of it's by products. That explains why it only happens when you gravel vac. Since the gas is being released from the pockets when you disturb it. Try adding a powerhead, or getting a more powerful filter to help circulate the tank, and get rid of the anaerobic bacteria. Hope this helped 😀

Edited by Warren Peace
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On 8/18/2021 at 10:01 AM, Warren Peace said:

If it smells like rotten eggs, it's probably Hydrogen Sulfide. Hydrogen Sulfide occurs when there is decomposing organic matter (fish food, dead plants, waste, etc.) Usually, anaerobic bacteria is the culprit. It occurs when there isn't enough flow. Since there isn't enough flow, and or, oxygen, it might be the anaerobic bacteria taking over, and using the fish waste, as the Hydrogen Sulfide is one of it's by products. That explains why it only happens when you gravel vac. Since the gas is being released from the pockets when you disturb it. Try adding a powerhead, or getting a more powerful filter to help circulate the tank, and get rid of the anaerobic bacteria. Hope this helped 😀

Hmm, interesting. This is my first foray into sponge filters. I have two co-op large ones set up on opposite ends of the tank. Figured two would help with flow and be a good back up in case I need to set up an emergency tank. 

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On 8/18/2021 at 11:01 AM, Warren Peace said:

If it smells like rotten eggs, it's probably Hydrogen Sulfide. Hydrogen Sulfide occurs when there is decomposing organic matter (fish food, dead plants, waste, etc.) Usually, anaerobic bacteria is the culprit. It occurs when there isn't enough flow. Since there isn't enough flow, and or, oxygen, it might be the anaerobic bacteria taking over, and using the fish waste, as the Hydrogen Sulfide is one of it's by products. That explains why it only happens when you gravel vac. Since the gas is being released from the pockets when you disturb it. Try adding a powerhead, or getting a more powerful filter to help circulate the tank, and get rid of the anaerobic bacteria. Hope this helped 😀

I agree but wanted to share this in case you have this issue. I used a resin tree root decoration recently…I did not look for air flow holes prior to using. When I lifted it the interior was waste and stagnant water that was anaerobic and noxiously rotten egg smells for the reasons @Warren Peace described  If you have decor check for flow through

Edited by Guppysnail
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On 8/18/2021 at 10:16 AM, Warren Peace said:

Do your have any floating plant perhaps? If there are too many floating plants, it could stop the oxygen exchange.

I do, frog bit, wisteria, and tiger lotus lily pads. It covers almost half my tank top.

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On 8/18/2021 at 10:26 AM, Guppysnail said:

I agree but wanted to share this in case you have this issue. I used a resin tree root decoration recently…I did not look for air flow holes prior to using. When I lifted it the interior was waste and stagnant water that was anaerobic and noxiously rotten egg smells for the reasons @Warren Peace described  If you have decor check for flow through

Thanks for the tip. I don't think I have this issue but I'll look closely to see if I'm missing anything. The smell came AFTER I started gravel vacuuming the substrate and it came heavily from the bucket it was going into. Of course, the tank smelled too but I figured I'd add that detail considering the tips provided.

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On 8/18/2021 at 8:01 AM, Warren Peace said:

If it smells like rotten eggs, it's probably Hydrogen Sulfide. Hydrogen Sulfide occurs when there is decomposing organic matter (fish food, dead plants, waste, etc.) Usually, anaerobic bacteria is the culprit. It occurs when there isn't enough flow. Since there isn't enough flow, and or, oxygen, it might be the anaerobic bacteria taking over, and using the fish waste, as the Hydrogen Sulfide is one of it's by products. That explains why it only happens when you gravel vac. Since the gas is being released from the pockets when you disturb it. Try adding a powerhead, or getting a more powerful filter to help circulate the tank, and get rid of the anaerobic bacteria. Hope this helped 😀

I'd second this analysis and advice.  My personal experience is that there's some types of substrate (e.g. the glossy epoxy coated stuff that a lot of chain stores sell as their house brand) that really seem to encourage the conditions for "tank stank".   @Warren Peace suggests what has worked for me:  1) Remove as much waste as you can, manually "deep turning" your substrate in the process.  My experience has been that anerobic bacteria seem to really like decaying plant matter when it gets into low/no water flow conditions,  so keeping up with plant trimming and removing loose/dying/dead leaves and stems will help. 2) Increase aeration/water surface agitation.  Adding burrowing snails to your tank will help scavenge additional waste/aerate the gravel as well...but I've needed a pretty large population of them to be effective (which can be unsightly).   Good luck!

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Dumb question time.  @Chad Do you have any wood/driftwood features in your tank by chance?  I had a situation with a piece of wood that I had purchased slowly starting to decay several months after putting it into a tank.  No smell for several months,  then a little hint of sulphur at water change time, and then full on "open a window" until I removed the wood and deep cleaned the gravel.

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On 8/18/2021 at 10:53 AM, NanoNano said:

Dumb question time.  @Chad Do you have any wood/driftwood features in your tank by chance?  I had a situation with a piece of wood that I had purchased slowly starting to decay several months after putting it into a tank.  No smell for several months,  then a little hint of sulphur at water change time, and then full on "open a window" until I removed the wood and deep cleaned the gravel.

That's a great question! I recently added some cholla wood when I added the shrimp. But I've had some spider wood in the tank for quite some time. Maybe 8-9 months now?

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For me that smell when cleaning your substrate is a call to go bare bottom. Cleaned gravel out of a few tanks and saw the signs of needing to move away from it. The first time I helped someone remove rocks from the bottom of their koi pond, I said no more. The amount of waste and bacteria hiding in those builds up and is just a nightmare waiting to happen for some folks. I compare it to a septic tank in hiding. Bare bottom has limitations but worth it IMHO.

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On 8/18/2021 at 10:01 AM, Chad said:

That's a great question! I recently added some cholla wood when I added the shrimp. But I've had some spider wood in the tank for quite some time. Maybe 8-9 months now?

In my case the "bad wood" gave off only a slight objectionable odor when it got exposed to air during water changes,  the strong odor came from the bucket that I siphoned the waste from the substrate into....which seems to mimic your situation.  Spider wood is widely used in the hobby and has basically no reputation for objectionable decay or odor,  so that pokes a pretty big hole in my hypothesis.   I'd give some of the other suggestions here priority and then try removing the wood maybe as a last resort.  Good luck- I know this is an unpleasant situation and makes some of the days in the hobby not as fun as they could be.

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 I appreciate all the insights, truly. I've been trying to figure out what's been making my fish "off". Clamped fins, some deaths, and then some doing great. Columnaris, parasites, water quality? Nope. My last theory was old tank syndrome, and everyone's advice kinda points to that a bit. With a heavily planted tank it's hard to really get into the substrate and not derail all the decorations and plants. I wonder if oxygenation might be a culprit? Better/more thorough substrate cleaning? More flow? These are all great pieces of advice. I've added a lot of floater plants to help offset nitrates as guppies do what guppies do. I've been doing 10% water changes every other day (any more and the shrimp die, ring of death hit the first time I did a 20% change). Maybe up that to every day for a week and see what happens? Corral and remove some floaters? Bump up the air to the sponge filters a bit? Seems to be a decent place to start. Thanks again everybody!

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I like the woodsy smell. In my organic soil tanks, I am moving away from using sand in my caps, and now prefer the most minimal gravel cap. This better allows the soil to breathe, and mulm to settle through the gravel, and enrich the substrate.

My outdoor tubs had way too much sand, and I dealt with septic smells when breaking them down last fall. I also saw the impact on plants, although the White Clouds were too bulletproof to care.

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I like the woodsy smell too, the "septic" smell on the other hand is not good. I just did a 10% water change and gravel vac. And yes, the septic smell was going strong. The sponges I squeezed out were heavy with the scent too. Once done, and everything settled down, I'm smelling soil again. I have that store-bought, black painted gravel from a pet store. 2 inches deep. It is what it is for now, I do like the look.

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  • 2 months later...

The same thing happened while trying to get my 10 gallon cycled. Turned out to be I was doing a fishless ghost feeding cycle and food was accumulating/decomposing in my filter. Cleaned the filter, vacuumed the gravel, tried a different way of cycling and have not had that problem repeat.

Your tank is obviously far more established than mine, so I seriously doubt this is your issue (maybe similar with any excess food decomposing though?) but more to show there are many root causes for the same issue sometimes

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@Jennifer VThis issue was a concern of mine a while back. I’ve since come to realize my tank was fine and gravel vacuuming the substrate was causing the smell. So it is normal and should not worry you. The tank usually smelled like soil. What I was actually dealing with was columnaris or something like it. Basically it took me a long time to piece together the problem and sadly by the time I figured it out the fish were gone except my pleco. But I’ve rebuilt and am enjoying the hobby again. My problems were due to impatience which led to shortening quarantine periods. Quarantine new fish for a month, no matter how good they’re doing. 

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There were fish stores I could identify by smell in my younger days. Chick and Barbs in Vineland, NJ, had a unique smell. So did Martin's Aquarium in Cherry Hill. I could have walked into either of those stores blindfolded and known where I was. I don't what caused those unique smells (water conditioner perhaps?) but different fish stores had different smells. 

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