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Help! My Aerobic System Smells!

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Fixing aerobic septic system smells

A common myth is that aerobic systems smell. Well, some do, but they shouldn’t! A smelly septic system is a sign of a problem, one that needs to be fixed sooner instead of later. Here’s what to do if your aerobic system smells.

Lack of oxygen is the most common cause

The most common reason for a stinky aerobic system is a lack of oxygen — your system has to have oxygen at all times so that the “aerobic” bacteria can survive and properly treat your wastewater.

When there is a lack of oxygen the bacteria die off, the wastewater gets little treatment, and causes odors when the system sprays onto your lawn.

There are additional factors that can cause odors, but a lack of oxygen is the first thing that is usually checked for in aerobic systems.

3 steps to getting rid of smells

  1. Be sure the power to your septic system is on. All aerobic systems are connected to electrical components that keep the system running, and the system needs to be turned on 24/7.
  2. Call your maintenance provider. He or she will check the aerator and other components which work in conjunction with the aerator to be sure they are operable.
  3. Give bacteria time to replenish. Once repairs are made, it may take several days for the aerobic bacteria to grow — and for the odor to dissipate.

Using a septic system additive is not necessary, and will not speed up aerobic bacteria’s recovery.

Know the do’s and don’ts of aerobic systems

Just like standard septic systems, aerobic systems need routine care and maintenance to keep them functioning properly.

Check out our list of do’s and don’ts for aerobic systems to make sure you’re taking proper care of your septic system.

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48 thoughts on “Help! My Aerobic System Smells!

  1. My air pump went out and it took a week to get another one and get it hooked up. I treated it wit chlorine for septic systems and flushed a bag of bacteria down the toilet. What else can I do? I really don’t want it to smell bad.
    Thank You
    Billy Carson

    • Billy,
      There’s really nothing else you can do except give it a few days to a week for the aerobic bacteria population to grow and increase. While your aerator was out, the bacteria likely died off. Its the lack of oxygen causing the odors, so now that the aerator is again hooked up, the smell should begin to dissipate.

  2. We had an aerobic system installed a year ago and our yard smells horrible and has since it was installed. They have changed the setting multiple times for the aerator. They added a carbon filter mushroom to the top of the Aerator tank. We’ve taken a drain camera down the clean out to make sure water hadn’t settled in the line. We’ve talked about the products I’ve used to clean with. Do you have any other suggestions? My kids would like to play in their yard again. Thank you for your help!

    • I’m sorry to hear you’ve had so many issues. Odors usually have to do with a lack of oxygen in the tanks. You’ve mentioned the main things I would’ve recommended. The other things that come to mind are: 1)check the air hose leading from the aerator to the aerobic tank for leaks or water build-up, 2)if there is a long distance between the aerator and the tank, be sure the aerator is large enough for the distance, 3) be sure you are not hydraulically overloading the system, 4) be sure . If you get it figured out, please leave another post as to help other with similar situations.

  3. I recently bought a house with an aerobic system. I have never had one before and was given no instruction although I did have an inspection performed before moving in. Lately, there has been a smell coming from the sprinklers. I watched some videos about maintenance and called the service number on the system. There were no chlorine tablets in the system when I looked (based on the instructions of the service provider) I added tablets and have been waiting to see if the smell goes away. As far as I can tell the air compressor does not have a problem – the alarm isn’t going off anyway. How long should I wait before I do something else?

    • Great question! Chlorine will not dissipate any smell, although you should be sure chlorine is always present to disinfect the treated wastewater. The smell is usually due to a lack of oxygen. If the air compressor is operable, then other investigation is needed. Each system brand works a little different, but some have diffusers or other devices at the end of the air hose that can get clogged up and need replacement. Sometimes an air leak at the air hose can occur too. There are many other causes too, so I would suggest contacting a professional. Even though the alarm is not on, there are other items that may need attention (just like you don’t wait for your check engine light to come on before your change your oil or check your tire pressure). Best of luck!

  4. We have four people living in our house but with the holidays coming we get an additional eight people staying for several days up to a week. The septic smells terrible with the additional load. Is there anything proactive I can to to help build up the bacteria before everyone arrives?

    • Assuming your have an aerobic system, there’s not a whole lot that can be done. Even if you put more bacteria in, you’ll be hydraulically overloading the system. When the wastewater moves through the system too quickly without any treatment or settling time, the bacteria wont be able to keep up and may get washed through the system as well. You could pump out all the tanks/compartments just before they get there, but then you’ll likely still have odors because there wont be any bacteria in the system. The only advantage to pumping it, is so that the sludge doesn’t get pushed to the pump tank as this can cause your pump to clog up, burn up, etc., which leads to expensive repairs. Try to spread out usage (staggering showering times [and making them quick], laundry times, starting the dishwater or laundry when you all leave the house, etc.). Best wishes!

    • Usually a smell in the bathrooms is more related to a venting issue within your plumbing, such as a dry p-trap or clogged up roof vent. I would recommend contacting plumber verses a septic company.

  5. I have an aerobic septic system installed. After a recent system pumpout I think I need to replace the bacteria. Where do I get more of this bacteria to add back in?

    • You do not need to add bacteria to the system. You will naturally add bacteria by using the restroom. If you REALLY want to put something down, the only safe thing is bakers yeast, but even then it is not necessary and probably won’t help much.

  6. We have an aerobic system and it has been smelling for about 6 mos. my maintenance company has been out twice and states everything is working properly. It has plenty of tablets in it. I had it pumped a week ago but now it smells even worse. Also noticed one of the concrete lids is broken off on the edging. Maintenance company said it wasn’t a problem that it was covering completely. Could it be leaking air. Should we replace concrete lid with updated lids.

    • An aerobic system should not smell, if the wastewater is being treated properly. Usually, an odor is related to a lack of oxygen – the aerobic bacteria require oxygen to survive – which in turn the aerobic bacteria treats the wastewater. There are several things that come to mind: is the aerator working, is the aerator putting out enough air, is the air line from the aerator to the tank ok (not leaking, etc.), is there a part at the end of the air hose that is clogged (not allowing air to flow from the aerator into the tank)? Those are the main things that come to mind. Pumping the tank will not solve the odor if its due to a lack of oxygen. Whether its recently pumped or just a lack of oxygen, the bacteria will need to re-populate – which usually takes a few days once all is up and running. Chlorine only disinfects the treated effluent, it will not solve any odors. As far as the lid: some lids chip on the side when being opened. You can replace it if it makes you feel better. There are regulations here that require secure lids, but every state and county is different. Have you tried getting another company out for a second opinion on all that you mentioned?

  7. We have an aerobic system. Nothing but trouble so far. We had to get a larger air pump, because we have 4 adults in the house. We had to get a new pump in the last compartment that pumps out the water to the sprayers. We still have a smell, continually. Never goes away. We had a new sleeve put in for the chlorine tables, because they were not dissolving. We have had it cleaned out 3 times in 2 years! Any suggestions. We have thought about even having it moved farther away from the house. We have spent a fortune and still have a smell.

    • How old is your system? All aerobic systems have parts that need to be replaced. If your system is 1-2 year old, then this seems like more than normal (as far as replacing parts), but if your system is older than that, it just may be wear and tear. However, having an odor is a different issue. The smell is usually related to a lack of oxygen in the aerobic tank or a lack of thriving bacteria. In most cases, the lack of thriving bacteria is due to a lack of oxygen, but if the aerator is operable (and everything related to the aerator has been checked – such as any air hoses, diffusers, etc.) then perhaps the bacteria is dying off for another reason. Does your household use a lot of chemicals or bleach? Is anyone on medication? This can cause bacteria to die off. Even a mixture of regular household things such as bath oils, tanning oils, dumping a lot of juice or soda down the drain, fabric softener, etc. can effect the bacteria and treatment. Also, if there are a lot of surges on the system (such as using a lot of water at one time), the wastewater may not be getting enough time in each part of the treatment process. You may just need to evaluate household usage, medications and surges…maybe you can pinpoint something that may be causing or contributing to the odors. Best wishes!

  8. Can you use yeast? I have heard this several times. We just moved into a rent house and the septic sprinklers smell really bad.

    • You can use yeast, although it won’t help with the odors from your spray heads. That’s usually related to a lack of treatment or lack of oxygen in the system (I’m assuming its an aerobic system). If the house has been vacant for a while, then there is not any wastewater to keep the aerobic bacteria alive. It may take a few days on average for the aerobic bacteria to populate again, once that occurs (if all else is functioning properly), then the smell should dissipate. If it does not, call a local aerobic system maintenance provider. Happy Thanksgiving!

  9. We replaced our hoses and aerator diffussers about a week ago and still have an odor when the sprinklers go off. I only use all natural cleaner and very little bleach, however I do use fabric softener and pour soda down the sink. If I stop these should it help with the odor? I’ve been told to put molasses and yogurt to build up bacteria. Does this help at all?

    • There’s no guarantee…but I’d avoid the fabric softener and pouring soda down the sink as they can effect the treatment. If you are using the system regularly, then you shouldn’t need to add anything to help build up the bacteria. Are you over-using the system or have a lot of surges of water? Is the aerator running normally? There’s not a one-size-fits-all answer, but it could be a combination of things.

  10. please help me out I have had several people come to my property to try and figure out the septic gas buildup in my home and outside and no one has an answer it is much worse during the cold weather 15 minutes after a shower or washing clothes or washing dishes septic gas comes up through the vents in the house even with the furnace off it comes up through the vents in fills my home every single day I have to put fans in my windows to draw out the septic smell it is overwhelming we have cleaned out the vent pipe by blowing air down through we have put a hose down through we have covered the septic access openings outside with garbage bags because the concrete lids are old and chipped the septic comes up through the drains in the garage also and in the storm sewer at the bottom of the road this is a nightmare and I am sure that it is going to cost thousands of dollars that i absolutely do not have….whatever the problem is but nobody can figure out what the problem is could it possibly be my aerator I have lived here for three years and no one has ever told me I needed a new one or even checked it .

    • If you are having smells INSIDE the home, it’s usually not from the septic or aerobic system. We usually recommend to contact a plumber to check the venting in the home and the pea traps. If you have old chipped lids on your tank, then its more likely that gasses would escape through any openings around the lid where its chipped and cause a smell outside (possibly), instead of up into your house. However, systems with old chipped lids usually do not have an aerator…do you know if you have an aerobic system? Even then, a non-functioning aerator would more likely cause odors OUTSIDE than inside.

  11. I have an aerobic system at my house. We have a problem with boggy yard and smell. 6 people in household. Showers dishwasher washing machine. We have 3 sprinkler heads. Have replaced the water pump, air pump and just installed new diffuser bar. There is tremendous turbulence in the tank with the airflow. Should I regulate the airflow? It also smells…loud. I’m thinking of installing an affluent filter and a liquid bleach dispenser for disinfectant. The water is grey. I dont see how it can clear up with all the turbulence. Thank you for your opinion.

    • Well that’s a lot of cover, but I’ll try my best to address as much as possible to the best of my knowledge and experience. Smell: an odor from an aerobic system usually is due to lack of treatment of the wastewater, but the question is why. The two most common reasons are lack of oxygen for the aerobic bacteria to thrive and over usage/surges on the system. So, if the air pump has been replaced and the diffuser is new, then we know the system is getting oxygen. How long ago were they replaced? It may take a few days + for the aerobic bacteria to re-populate so if they were just replaced, you may want to give it some more time to see if the smell dissipates. The other part is over usage on the system. 6 people is a lot of residents, so I’d check on your system size and treatment capacity. In Texas, systems are sized for a maximum Gallons Per Day (GPD) in treatment capacity. If you can find out the system treatment capacity in GPD, and find out your actual GPD for your family, that can help guide you to see if you are over-using the system for its size/design. Being that your yard is “boggy” (soggy?) then that may give indication of more water being discharged than designed if its staying wet. Also be sure the spray area has not been reduced from its original design. As far as the turbulence goes….I don’t know what system brand you have, but for the systems we install, there is a constant “rolling” of bubbles in the aerobic tank that is needed. So I’m not sure if the turbulence you are referring to is normal or not, or if its turbulence from over-usage. Also, check for dripping faucets, running commodes, malfunctioning water softener (if connected) as that can put extra water into the system. All aerobic systems in Texas have to have a disinfection device – most are chlorine – some are UV light. I’d bet you already have some sort of disinfection device, but chlorine usually does not treat the odor issue. An effluent filter may be helpful if there is a lot of debris passing from one tank to another, but be sure to clean the filters regularly so they don’t get plugged up an cause backup.

  12. We have a Mircrofast 625 system and it has smelled since being installed a year and a half ago. It is sized to treat 625 GPD which should be plenty large. The water that comes out at the end of the system smells perfectly clear but there is an odor from the tank itself that we can’t get rid of. Since the systems works by having a fan blow air into the primary waste tank, I am wondering if it smells because the air also has to leave the tank. Should we pipe this air (not sure how) up above our heads? The waste is then pumped to a holding tank and then out to an underground drip system. So, in a sense, the system is working because the water is clear by the time it is put back into the environment, but the tank is near the house and stinks. We’ve tried covering it with carbon filters and cedar chip but it only makes it slightly better. Neither the installer nor the manufacturer have been helpful.

    • I can’t say I’m familiar with your system type (Microfast) so I cant offer much advice. If this is a type of aerobic system, you shouldn’t have a sewage-type odor, but a slightly musty smell can be normal. Maybe get another installer or a licensed service provider to come evaluate and give you another opinion.

  13. Our aerobic system (Hoot) was installed in 1998 and overall it has performed perfectly. I’ve had to replace the air pump about every 5 years and when it fails – it just stops. Over the last 6 months we have been getting a slight smell that we’ve never had before. I started investigating and I found that roots had grown into the conical lid in the middle tank. This is the tank with the air pump pipes.

    I removed as much of the roots as I could, and cut off the rest so the lid seats perfectly. We had all three tanks pumped. The smell returned when the tanks returned to normal levels.

    The pump is still working (and the green light is on). Looking in the tank I don’t see bubbles surfacing. Should I see bubbles or some agitation in the water surface?

    I don’t know:
    1. Is the air pump producing enough volume?
    2. How can I tell if the diffusers at the end of the pipe are clogged?
    3. Can I use my air compressor and force air into the pipe to unclog the diffuser?

    Thanks for any help.

    • Hoot systems are a little different than the Clearstream Systems we work on, so my answers are more relevant to Clearstream parts. You’ll typically see bubbling from the aerator. You could check the amps that the aerator is putting out. Diffusers: on Clearstreams, you have to pull out the air hose to get to the diffuser – we usually rotate between cleaning the diffuser and replacing the diffuser every 4 months (clean the diffuser, in 4 months replace it, in another 4 months clean it, and so on). To clean it we scrape off the sludge that has clinged to it. I’m not exactly sure about Hoot systems, but you may be able to find some diagrams online or videos on YouTube.

  14. I read the thread from the guy who moved to New York from Texas. Ironically, I love only about 20 miles from him and have had a similar problem. The difference is that my system is brand new, but for the life of me I couldn’t figure out the reason for the smell, or other septic-related issues such as “burping” toilets…until today. It gets maintained by a technician every 3 months I believe, yet he somehow has missed this for 3 years, just like me. When I pulled off the cap with the aerator on it, I noticed that the aerator pvc didn’t actually go all the way through the cap. On the outsode it appeared fine, but when molded, concrete covered the inner end of it, therefore the system couldn’t breathe as designed. Instead, it was forced to pull air from around the sides of the cap, which is clearly insufficient. Maybe this guy from Texas has the same issue. Just pull that lid off and make sure the pvc aerator isn’t blocked off. I just used a hammer to break off the thin layer of concrete causing the obstruction. Hope this helps someone.

  15. I apologize for the amateur question but I’ve been unable to pull the diffuser out of the tank for inspection and possible replacement. I’ve turned off the pump, disconnected the pvc linked to the aerator but no matter how I try to angle the pipe I’ve been unable to pull up the diffuser end. I understand the tank has a narrow opening and the diffuser is to one side but I’ve been unsuccessful so far. Is there a trick to pull it up? The smell has increased slightly last couple of months and I wanted to check this first before calling for maintenance.

    • Not sure what brand of system you are referring to…the answer may be different for each brand. Sometimes the diffusers are difficult to pull out and sometimes the diffuser breaks off the end of the hose while they are being removed, in which case the diffuser is replaced. Sometimes it just cant be helped. We recommend the diffuser to be replaced about every 8 months or so. So, if its been longer than that and the diffuser breaks off, then you need to replace it anyway. Just be aware that if the diffuser hasn’t been changed in a while, once it is changed it could affect the aerator with the change in pressure. Hope that helps.

  16. i have irrigation system in garden which is fed with effluent treated water. It smells offensive the moment irrigation system starts. Kindly guide if there is any chemical treatment

    • I hope it’s not a vegetable garden! The treated effluent should not smell foul. Odors are usually caused by a lack of treatment of the wastewater – usually chemicals such as chlorine only serve to disinfect properly treated effluent. I’d get a professional to check all the components of your system and be sure the system is receiving enough oxygen for treatment (assuming this is an aerobic system).

  17. Good morning,
    I have a Norweco Singulair 780 installed in 1990. I purchased this home two months ago, and I can periodically (every 3-4 days) smell a slight to fair smell of rotten egg down-wind from the septic tank. Two weeks ago, I discovered the aspirator tip was cracked and only had two prongs left. I replaced it at that time with a non-NSF approved shaft/tip (to match the LEM1800 motor already installed by previous homeowner). I have 2 adults, and 3 children taxing the system.

    In reviewing the aerator pumps for this system, I was told the NSF approved Singulair 206c has a shorter shaft length than its predecessor. Could I be having insufficient oxygen due to the non-NSF approved aerator?

    The lid to the aerator tank is also cracked and crumbled on the perimeter. Could this be a contributing factor?

    I have been following the basic do’s and dont’s of the system, but on few occasions we may have exceeded the 500gpd limit. Could this be a contributing factor to several days of stink?

    Before I spend $800 on the Singulair 206c aerator and new control panel, I’m hoping some feedback might point me in the right direction. The odor is strong enough to make it uncomfortable to keep windows open or to spend time in my front yard.

    Thanks for any feedback

    • Aerobic system parts require NSF approval for a reason, so that may be part of the issue (if its doesn’t meet standards). Odors are usually due to a lack of treatment, which in most cases is due to a lack of oxygen…so this may be a puzzle piece in your situation. I would recommend replacing the cracked aerator lid, although that may not be causing the smell, I’m sure that may be allowing some odors to escape which may be why you smell the odors. Overloading the system, using more GPD than the system was rated for, could certainly also affect the treatment of the wastewater. Above all, I’d really recommend finding a reputable and experienced person to check the system and give you more guidance.

  18. Hi Courtney. Thanks so much for the great info. I’ve read your responses but I have a weird problem. Our aerobic stinks inside our house. I saw your comment that it’s more than likely a pea trap issue or a venting issue. The company that installed the system keeps telling us to bleach the heck out the system and has me putting in bleach down drains and several different spots outside. I am going to check our venting. It’s killing me. It’s a new home and smells like the sewer. Now, here’s the weird part. The smell happens every night between 10 and 11pm. No smell during the day. But come 10:01pm and the smell starts. What the heck is happening? Also, I don’t think our washer line out has a pea trap. Fatal? Anyhow, I would love any advice but have a feeling you’re going to tell me it’s a pea trap or venting issue.

    • Odors inside the house are usually not from a septic or aerobic system, so I’d rule out the possibility of venting issues. Putting a ton of bleach down the drains will kill off the good bacteria in the system that is needed to treat the wastewater, so that doesn’t sound like something we would ever recommend. The only place bleach should go is into the chlorinator. Are you spray heads spraying between 10am and 11pm when you notice the odor? You will have odor outside if your system is not treating the wastewater (such as killing off the bacteria population by adding bleach), but that usually will not cause the odor outside.

  19. Aloha,
    We have an aerobic system that does not have a dedicated area to allow the treated water to settle. From the top the tank appears just like a regular septic. The side where the effluent enters is baffled so as to keep away the “floaters”. The second compartment is aerated. The tank level is controlled by level switches and a sump style pump. When level goes higher, the aerator stays off for a time to allow the water to settle, then the pump pumps, then the aerator starts back up and the cycle begins again. My question is how long can the aerator stay off? We have no odors but sometimes the effluent is not clear so would like to leave the aerator of longer. Should I just experiment until I start smelling?

    Thank you.

    • Hi Richard. I am not familiar with the set up you are explaining. The aerobic systems we deal with have aerators that need to run 24/7. Have you asked any local installers in your area?

  20. Can you tell me how to check the air pressure for a diffuser I was told They needed to be cleaned that the pressure was high but I’m not sure how they check this The system is fine and there is no smell from the tanks

    • You’ll need to check the psi. The diffuser needs to be replaced at least every year. In addition to cleaning diffusers when needed, our company practices is to replace the diffuser every 8 months. The diffuser cannot be cleaned well once there is too much sludge on it, so its best to replace them. They are low in cost, but can lead to a domino effect of expensive repairs if the diffusers are not taken care of. Don’t wait until you have odors, by then your system is not treating the wastewater effectively…you don’t want it to get to that point.

  21. What can I do in the winter time to keep the drain line on my Norweco system from freezing? The drain line freezes and then the odor follows.

    • Which “drain line” are you referring to? Are you in a region that freezes often? Where do you get the odor?

  22. Hi Courtney,

    Thanks for the reply. I discovered today that my backwash pump has failed. Not a freezing issue as first suspected. Thanks again, Tim

  23. Our septic aerator broke and we aren’t sure how long it wasn’t functioning before replacing it. We just replaced it and now there is a horrible smell in the bedrooms nearest to the septic system outside. Is this normal? How can we fix it?

    • Now that there is aeration in the tank, the aerobic bacteria have to repopulate and its normal to have a smell outside for a few days but it should dissipate. Usually there is no smell inside the house, unless you possibly also have a clogged roof vent for your plumbing that is not letting the gasses escape through the vents. You could wait a few days and see if the smell dissipates. If it does not, you might want to call a plumber to check the venting.

  24. I just replaced my air pump, and it smells horrible. I understand that I need to give it a while for the bacteria to grow, however, I can hear air bubbles under one of the round green covers. I’ve never heard it before. Is this normal after a replacement of the air pump? If so, should it go away? Just to elaborate, I replaced the pump just an hour ago. Any help would be great. Thanks in advance.

    • Yes, you should hear the bubbles under the lid for the aerobic tank, this is normal. The air pump you replaced pumps air into the tank. If you never heard it before, perhaps you just never noticed it or perhaps the air pump has been weak or out for some time. When the system does not have oxygen, the wastewater turns “septic” and is not getting treatment as the system has to have oxygen 24/7 for the aerobic system to thrive and treat your wastewater. It usually takes a few days for the aerobic bacteria to re-populate, so it is normal to have an odor for a few days. If the odor does not dissipate, contact a licensed maintenance provider to see if there is something else that is going on, or if the system needs to be pumped.

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