Sump aeration

[Dirtyshoez]

Been reading the forum and I know why we don't use aeration in saltwater tanks. But would this be the same concept in a sump aswell with proper maintenance.

My idea is to use it temporarily during a lights out cycle while killing off algae to create oxygen in the water.

 

[Subsea]

I use air stones in my reef tank. Salt creep is not a problem for me.

 

[P-Dub]

Been reading the forum and I know why we don't use aeration in saltwater tanks. But would this be the same concept in a sump aswell with proper maintenance.

My idea is to use it temporarily during a lights out cycle while killing off algae to create oxygen in the water.

There have been multiple threads about this. It is referred to as 'Bubble Scrubbing' if memory serves me correctly. I did it for several years in my sump at the last chamber, so the bubbles get further chopped up by your return pump. You go through a lot of balsa wood airstones. The idea is to have many, many tiny bubbles create a cloud of bubbles in your DT to bind with crud in suspension or on the coral tissue surfaces. It then floats to the surface and gets skimmed off to be caught by your filter socks and protein skimmer. It increases O2 saturation, and you end up with a really clean tank. The one caveat is that you have to have very strong flow periods in the DT to prevent air accumulation under any corals that can hold it, like plating corals. Search bubble scrubbing.

 

[Fish Fan]

Been reading the forum and I know why we don't use aeration in saltwater tanks.

Did you read that here at R2R? That's more of a freshwater planted thing

You necessarily need a lot of aeration in a saltwater tank for good gas exchange. You absolutely can use air stones, though they can cause salt creep, but that's not impossible to work around. You can also get gas exchange by having circ pumps breaking up the water surface, and if you have one a protein skimmer is a good source of aeration, though a protein skimmer is not required for a successful tank.

Good luck!

 

[Jamie814]

It is referred to as 'Bubble Scrubbing'

It makes sense that it would help clean the display of some floating particles by them sticking to the air bubbles and rising to the top of the tank and into the overflow.

Organics stick to the bubbles and rise to the top inside a skimmer, as the bubbles rise to the top of the skimmer they "pop" and the organics end up stuck on the walls of skimmer cup or over the top and into the collection cup.

An air stone really does not do anything different than a skimmer when it comes to gas exchange.

 

[Reef Jedi]

You can run air stones but as mentioned before and in my experience you will get a good amount of salt creep. Gas exchange in a skimmer is an a+ way to do this while pulling out organic materials.

Ever notice salt tanks in hospitals usually always have an air stone in them? They almost always use canister filters and the air stone helps oxygenate the water since the canister filter is a closed loop. I serviced tanks on and off for 10 years through Highschool and college mainly for commercial accounts and some residential.

 

[P-Dub]

An air stone really does not do anything different than a skimmer when it comes to gas exchange.

This is true, more or less. Airstones will accelerate gas exchange when employed in a "bubble scrubber" configuration. It really depends on what you are trying to accomplish. Higher gas exchange and inevitably higher O2 saturation will generally lower co2 levels, provided the source air while performing the bubble scrubbing function is low in co2. I used co2 scrubbing media, (read sofnolime or the kind) in a large canister filter as the draw air for an enclosed air pump, all situated at the exterior of my home. When I stopped using the bubble scrubbing, I still used the co2 meda canister to filter the draw air for my skimmer. Again, the draw air was from the exterior of the home so the source air for the skimmer has the lowest to no CO2, as long as the media was not exhausted.

 

[Dirtyshoez]

This is true, more or less. Airstones will accelerate gas exchange when employed in a "bubble scrubber" configuration. It really depends on what you are trying to accomplish. Higher gas exchange and inevitably higher O2 saturation will generally lower co2 levels, provided the source air while performing the bubble scrubbing function is low in co2. I used co2 scrubbing media, (read sofnolime or the kind) in a large canister filter as the draw air for an enclosed air pump, all situated at the exterior of my home. When I stopped using the bubble scrubbing, I still used the co2 meda canister to filter the draw air for my skimmer. Again, the draw air was from the exterior of the home so the source air for the skimmer has the lowest to no CO2, as long as the media was not exhausted.

I ordered a co2 scrubber. I opened my windows up the other day and saw a little bit of a difference. Also have a couple of dogs so I'm not sure if this plays a role.

 

[P-Dub]

I ordered a co2 scrubber. I opened my windows up the other day and saw a little bit of a difference. Also have a couple of dogs so I'm not sure if this plays a role.

You'd be surprised just how high your indoor CO2 levels are. We have two adults and 5 dogs. My algae loves the indoor air "quality"

 

[bushdoc]

Aeration of saltwater tank is best achieved by means of powerheads preferably making turbulent flow and sump/display tank return and also protein skimmer.
Freshwater aquarists use air stones primarily because they cannot have such a high flow as in marine aquarium. Using air stones in reef tank is not the most efficient method to oxygenate water.

 

[P-Dub]

Aeration of saltwater tank is best achieved by means of powerheads preferably making turbulent flow and sump/display tank return and also protein skimmer.
Freshwater aquarists use air stones primarily because they cannot have such a high flow as in marine aquarium. Using air stones in reef tank is not the most efficient method to oxygenate water.

Weeeeelllll… that’s debatable.


As with most things in reefing, it really depends on what you're trying to accomplish and how you're implementing it. Gas exchange primarily occurs at the air-water interface, so if your goal is simply to improve gas exchange efficiently, then yes, you're basically correct, but airstones can still help.
But let’s dig a little deeper.
If you already have good surface agitation and a protein skimmer running, and you're still looking to lower CO₂ levels or increase the air-to-water contact ratio, adding airstones to the sump is a solid option. It’s a manageable way to boost gas exchange without the mess of salt creep in the display tank (DT). Salt creep in the sump is much easier to deal with. Pairing this with a CO₂ scrubber can further improve results.
In this case, the OP is trying to address an algae issue and wondering if additional gas exchange via an airstone will help. The short answer: yes, it can. But how effective it will be — and what downsides might come with it — depends on your setup.
For example, in my own tank, increasing surface agitation by adding more wavemakers or ramping up flow intensity would cause water to splash over the rim, creating bigger problems than it solves. So for me, airstones in the sump offer a low-cost, low-risk, and temporary way to improve gas exchange.
So go for it, @Dirtyshoez — toss an airstone or two in the sump and see how it goes. Let us know what you find, even if it’s anecdotal. Every tank is different, and your experience might help others in similar situations.

 

[bushdoc]

Weeeeelllll… that’s debatable.


As with most things in reefing, it really depends on what you're trying to accomplish and how you're implementing it. Gas exchange primarily occurs at the air-water interface, so if your goal is simply to improve gas exchange efficiently, then yes, you're basically correct, but airstones can still help.
But let’s dig a little deeper.
If you already have good surface agitation and a protein skimmer running, and you're still looking to lower CO₂ levels or increase the air-to-water contact ratio, adding airstones to the sump is a solid option. It’s a manageable way to boost gas exchange without the mess of salt creep in the display tank (DT). Salt creep in the sump is much easier to deal with. Pairing this with a CO₂ scrubber can further improve results.
In this case, the OP is trying to address an algae issue and wondering if additional gas exchange via an airstone will help. The short answer: yes, it can. But how effective it will be — and what downsides might come with it — depends on your setup.
For example, in my own tank, increasing surface agitation by adding more wavemakers or ramping up flow intensity would cause water to splash over the rim, creating bigger problems than it solves. So for me, airstones in the sump offer a low-cost, low-risk, and temporary way to improve gas exchange.
So go for it, @Dirtyshoez — toss an airstone or two in the sump and see how it goes. Let us know what you find, even if it’s anecdotal. Every tank is different, and your experience might help others in similar situations.

Did you check oxygen content in the water before and after adding air stones?

 

[P-Dub]

Did you check oxygen content in the water before and after adding air stones?

Just to clarify — I don’t (and didn’t) have a DO probe or a PM3 module on my Apex, so I can’t provide hard data on dissolved oxygen levels. That said, I do believe that my method of bubble scrubbing had a net positive effect on O₂ concentration and CO₂ reduction, based on observable results.
I scrubbed with lights out, using a high-volume air pump to push CO₂-scrubbed air from outside the house into four large wood airstones placed in the return section of my sump. The result? A dense microbubble cloud that was so thick, you couldn’t see the back of the tank — it looked like fog. The return pump further chopped up the bubbles as they entered the display tank.
While I can’t quantify the exact impact, the visual density of CO₂-starved air and the sheer volume of bubbles suggest a meaningful increase in gas exchange. Anecdotally, it had to help — especially compared to normal operating conditions, and I believe it would help in your case as well, just not to the same level, of course.

 

[BryanM]

I've not aerated my sump, but I have put a powerhead in there to move water around, which somewhat also does the same thing. And I'm an algae turf scrubber guy that pumps are in to the chamber of the ATS, so there's more air there too.

 

[P-Dub]

I've not aerated my sump, but I have put a powerhead in there to move water around, which somewhat also does the same thing. And I'm an algae turf scrubber guy that pumps are in to the chamber of the ATS, so there's more air there too.

Definitely effective, to varying degrees.
Refugiums help with nutrient and CO2 uptake. Algae scrubbers do the same with the added benefit, depending on their design, of variably increasing gas exchange.

 

[Dirtyshoez]

You'd be surprised just how high your indoor CO2 levels are. We have two adults and 5 dogs. My algae loves the indoor air "quality"

It's pretty crazy to think about really.

 

[mcarroll]

Been reading the forum and I know why we don't use aeration in saltwater tanks. But would this be the same concept in a sump aswell with proper maintenance.

My idea is to use it temporarily during a lights out cycle while killing off algae to create oxygen in the water.

What??!! We use aeration!! ;)

Surface skimmers, protein skimmers, circulation pumps – we've got aeration turned up to 11! Air stones are down at a 3 or 4.

Saltwater tanks are usually reef tanks these days. And reef tanks have bomb aeration (or they don't work).

Fish tanks, by contrast, ususally have low flow and LARGE bio-mass – dissolved oxygen levels can be concern.

The protein skimmer, BTW, was created as an airstone container when saltwater aquariums took off in the 1960's. Don't believe the hype – salt creep is REAL! ;)

And don't get it confused – aeration is to assure gas exchange. It is NOT to lower CO2 levels or remove CO2 from the water....as if CO2 is bad for some reason. It is not.

The only exception is if your HOUSE really has CO2 levels building up to high levels – like 1000 ppm.

That is VERY rare, but if it's really happening you need to get your house fixed, not your fish tank. Corals use CO2 for photosynthesis, so they like it. Human healths suffers though!!

The only and only REAL case of high-CO2 I've seen on here, the user actually verified it, called an HVAC company and had a change made so they get more fresh air in the house. The user IMMEDIATELY felt an improvement in their own health.

So CO2 scrubbers aren't the answer, no matter what. Corals don't care, and that's not the way you fix that issue if it's a real issue. (Most folks are just chasing numbers.)

 

[P-Dub]

What??!! We use aeration!! ;)

Surface skimmers, protein skimmers, circulation pumps – we've got aeration turned up to 11! Air stones are down at a 3 or 4.

Saltwater tanks are usually reef tanks these days. And reef tanks have bomb aeration (or they don't work).

Fish tanks, by contrast, ususally have low flow and LARGE bio-mass – dissolved oxygen levels can be concern.

The protein skimmer, BTW, was created as an airstone container when saltwater aquariums took off in the 1960's. Don't believe the hype – salt creep is REAL! ;)

And don't get it confused – aeration is to assure gas exchange. It is NOT to lower CO2 levels or remove CO2 from the water....as if CO2 is bad for some reason. It is not.

The only exception is if your HOUSE really has CO2 levels building up to high levels – like 1000 ppm.

That is VERY rare, but if it's really happening you need to get your house fixed, not your fish tank. Corals use CO2 for photosynthesis, so they like it. Human healths suffers though!!

The only and only REAL case of high-CO2 I've seen on here, the user actually verified it, called an HVAC company and had a change made so they get more fresh air in the house. The user IMMEDIATELY felt an improvement in their own health.

So CO2 scrubbers aren't the answer, no matter what. Corals don't care, and that's not the way you fix that issue if it's a real issue. (Most folks are just chasing numbers.)

I could debate a few of your points, but I’ll keep it brief and focus on two key areas:

1. CO₂ is a real concern in reef aquariums.
   When CO₂ dissolves in seawater, it forms carbonic acid, which lowers pH — a process known as acidification. In a closed system like a reef tank, this can have significant effects on coral health and calcification. This is even more important, for example, when running a calcium reactor, where monitoring pH becomes critical. Adding an airstone to the reactor’s effluent chamber is a well-known method to help off-gas excess CO₂ and stabilize pH — not always necessary, but definitely good practice depending on your setup.
2. CO₂ scrubbers can help with pH stability.
   While corals do use CO₂ for photosynthesis, excess CO₂ in the water can displace dissolved oxygen, leading to symptoms of oxygen deprivation in fish — rapid breathing, gasping at the surface, etc. This is rare in a well-maintained system, but during a power outage or in high bioload tanks, it becomes a real risk. CO₂ scrubbers, when used properly, can help maintain a healthier pH range and improve overall gas exchange.

So yes, aeration is primarily about gas exchange, but in reef tanks, that exchange includes managing CO₂ levels to maintain stable pH and oxygenation. It’s not just about chasing numbers; it’s about understanding the chemistry and biology of our systems.

 

[mcarroll]

Coral care much more about fundamentals being correct then about pH.

Strong flow and aeration are two hallmarks of reefing ever since the Berlin system traveled over to the USA. ;)

If you have a reef tank that some air stones can make a difference in... I think there was something wrong with the tank formula.

Live rock and a protein skimmer plus strong flow and lighting.

That is the long-standing formula.

The protein skimmer is already a supercharged air stone.... and modern (c2000+) powerheads create tons of circulation and surface disturbance.

Even a half baked reef tank has great aeration tgese days.... compared to any traditional fish only tank, where this could be a more daily concern.

Of course there are exceptions where you could use something like a CO2 scrubber (eg) in an emergency...

The overarching point is this is not done for corals, they benefit from carbon dioxide in the water. If you have this problem, it should be rectified for your own personal health… The tank will benefit as a side effect. I was trying not to gloss over the personal health angle of this.... and encourage people not to chase numbers. Both.

The only time it is not chasing numbers is when your household carbon dioxide levels are so high that they actually do cause the tanks pH to be too low. look around at all of the stellar awesome reef tanks that there have been over the years that run at fairly low pH ranges without any perceivable problem though before you decide what "too low" is. Coral skeletons are often brought up in this area of the conversation, but coral skeleton is biogenically synthesized by the coral, and is independent of the pH of the water. Corals do not care about the water's pH... they care about the fundamentals underneath that number, carbon dioxide, carbonate, availability, etc.

If you are someone who actually perceives that you have a carbon dioxide issue in your living space (and you notice it because you are monitoring your tanks pH), I would verify the problem with the carbon dioxide meter first, and if confirmed, rectify the problem with the living space and get more fresh air. Don't simply fix the fish tank pH.

 

[P-Dub]

Coral care much more about fundamentals being correct then about pH.

Strong flow and aeration are two hallmarks of reefing ever since the Berlin system traveled over to the USA. ;)

If you have a reef tank that some air stones can make a difference in... I think there was something wrong with the tank formula.

Live rock and a protein skimmer plus strong flow and lighting.

That is the long-standing formula.

The protein skimmer is already a supercharged air stone.... and modern (c2000+) powerheads create tons of circulation and surface disturbance.

Even a half baked reef tank has great aeration tgese days.... compared to any traditional fish only tank, where this could be a more daily concern.

Of course there are exceptions where you could use something like a CO2 scrubber (eg) in an emergency...

The overarching point is this is not done for corals, they benefit from carbon dioxide in the water. If you have this problem, it should be rectified for your own personal health… The tank will benefit as a side effect. I was trying not to gloss over the personal health angle of this.... and encourage people not to chase numbers. Both.

The only time it is not chasing numbers is when your household carbon dioxide levels are so high that they actually do cause the tanks pH to be too low. look around at all of the stellar awesome reef tanks that there have been over the years that run at fairly low pH ranges without any perceivable problem though before you decide what "too low" is. Coral skeletons are often brought up in this area of the conversation, but coral skeleton is biogenically synthesized by the coral, and is independent of the pH of the water. Corals do not care about the water's pH... they care about the fundamentals underneath that number, carbon dioxide, carbonate, availability, etc.

If you are someone who actually perceives that you have a carbon dioxide issue in your living space (and you notice it because you are monitoring your tanks pH), I would verify the problem with the carbon dioxide meter first, and if confirmed, rectify the problem with the living space and get more fresh air. Don't simply fix the fish tank pH.

You make some solid points about the fundamentals of flow, aeration, live rock, and skimming are indeed core to reefkeeping, and the Berlin method laid a strong foundation. But reefing has evolved, and so have the challenges we face in modern home environments.
Regarding CO2 and pH, you're absolutely right that corals rely on carbonate chemistry, not just pH as a number. But pH is a reflection of that chemistry, and in a closed system like a home reef tank, elevated indoor CO₂ levels can significantly depress pH. As I’ve mentioned before, this isn’t just about chasing numbers; it’s about maintaining a stable environment where calcifying organisms can thrive.
Yes, corals synthesize their skeletons biologically, but the availability of carbonate ions, which is directly affected by pH, plays a major role in how efficiently they can do so. Lower pH means fewer carbonate ions, which can slow growth and reduce resilience.
While protein skimmers do contribute to gas exchange, they don’t always fully offset the effects of high ambient CO2, especially in tightly sealed, energy-efficient homes. That’s where CO2 scrubbers and strategically placed air stones can actually make a meaningful difference. Not because the tank is broken, but because the environment around it has changed.
And yes, if your home has CO2 levels consistently above 1000 ppm, that’s a health concern and should be addressed. But in the meantime, tank-level solutions like scrubbers and aeration can help stabilize pH while working on the root cause, which often can’t be easily or economically resolved to meet the needs of a reef system.
We don’t implement these solutions out of desperation or in ignorance of the fundamentals. We do so to augment their efficacy. It may be short-sighted to dismiss or diminish evidence-based, effective solutions simply because they don’t meet a subjective threshold of necessity.
So while I agree that chasing numbers for the sake of it isn’t productive, understanding what those numbers represent and how they affect coral health absolutely is. It’s not just about the tank formula anymore; it’s about adapting that formula to modern living spaces and the nuanced needs of our reef inhabitants.
And with that, I think we have fundamentally beaten this horse to death. If you disagree with what I have stated thus far, and it seems you do, well, we will agree to disagree, and I wish you the best in your reefing journey.

Peace.