Surface agitation

[BarrWarr]

Hi all,

I'm just wondering how important surface agitation is in a low tech/low light set up? Due to having a Betta and some Ember tetras, I've had to position the outflow so that the fish aren't subjected to too much flow as they were seemingly finding it a bit much previously.

The current position of the outflow nozzle suits the fish perfectly but there is virtually no surface agitation. I do have an air stone at the opposite end to create some agitation and the roots of my frogbit at the opposite end to the outflow are swaying so it seems there is sufficient circulation.

Do I need to address the lack of surface agitation? Plant wise, I only have Java fern, anubias and bucephalandra.

Many thanks.

 

[Bradders]

Due to having a Betta and some Ember tetras, I've had to position the outflow so that the fish aren't subjected to too much flow as they were seemingly finding it a bit much previously.

Just been going through the same challenge! New tiny fish meant my Biomaster 850 was too powerful with a certain lily pipe intake. (It has huge amounts of slits). Just swapped to a Chihiros which has under half the slits and slows the flow. I could have done this on the oase, but hey, it's just another reason for me to fiddle around with stuff. 🙂

The current position of the outflow nozzle suits the fish perfectly but there is virtually no surface agitation. I do have an air stone at the opposite end to create some agitation and the roots of my frogbit at the opposite end to the outflow are swaying so it seems there is sufficient circulation.

Now, some genius told me about the Betta challenges in fairly low plant mass tanks. If you are a little worried, you can shoot the outlet water down a pipe, whilst the airstone counteracts that with an upflow of bubbles in the same pipe. This causes a lot of turbulence and oxygenation, but does not result in a lot of flow. Can't say that I have done this personally, but it sounds like a plausible solution to the 'oxygenate but with limited flow' challenge.

 

[Connswater]

air stone

This is a source of much debate. A lot actually.

Lots of information and conflicting opinions. My humble view, if your submerged plants grow, rather than slowly perish, they will release oxygen when the lights are on, photosynthesis. In such circumstances, an air stone, should: with low animal stocking; genuine tropical fish in the tank; and, modest temperatures; prove unnecessary. Keep however, high oxygen demanding temperate fish and you will need air stones in my experience.

Once the lights have been off for a few hours the plants start on respiration, thus an air stone may well be very helpful to the fish. CO2 injection and an air stone when the lights are on seems counterproductive to me, especially if there are fast growing 'oxygenating' plants present. In my tank, once the lights have been on for a hour or so, you can see 'pearling', oxygen moving up leaves and being released. But since you aren't using CO2 an air stone isn't driving out injected CO2. Pearling can happen in low tech tanks, especially with plants like hornwort and egeria.

Lights off in a low tech tank, however, things may still be problematic for livestock. However, only in hot weather have I ever had need of an air stone.

Surface agitation, if it is not excessive (I know, define excessive?) is helpful, less debate on that as far as I can see, hence the use of lily pipes to gently move the surface and push via flow CO2 round the tank. The out put water from large filters will inevitably have more CO2 dissolved than the intake water thanks to the aerobic bacteria and their respiration, so a balance is wanted in a planted tank without injection of CO2, between driving out CO2 during the day and, coping with the lack of oxygen from the plants at night. Fish in pools die from low oxygen levels in hot weather and this often happens during the night. I am baffled by the popularity of solar operated fountains to increase oxygen.

Hope that is helpful someone more scientific than me may have a clearer and more erudite perspective.

 

[BarrWarr]

Thanks both. My tank is only 60ltr but is quite densely planted. I've spent way too many hours trying to get the right balance but finding it extremely difficult! I have an Oase filtosmart 100 so I can reduce the outflow but even at the lowest setting, it's still seemingly impossible to get the right balance for fish/agitation.

Up until a week ago, I only had the Betta and he stayed on one side due to the flow (which did create adequate agitation). I then added some Ember tetras and they stayed out of the flow too so I tweaked the position of the outflow and both seem much happier. Naturally, I don’t want any tank inhabitant to suffer (fish, plants, inverts) so I’m just trying to find the right balance and if having very little surface agitation over the majority of the tank is ok, I’ll be delighted. If not, I’m hoping there’s an easy solution!

 

[MoFish]

What kind of outflow do you have?, I also have a betta and small fish but things seem fine with my glass lily spin outflow.

 

[Andy Pierce]

Surface agitation, if it is not excessive (I know, define excessive?) is helpful, less debate on that as far as I can see

I think surface agitation is vastly overrated. That's one of those things that just seems conventional wisdom / obviously correct but I just don't understand how the actual agitation (vs water flow itself) can make much difference.

 

[Bradders]

I think surface agitation is vastly overrated. That's one of those things that just seems conventional wisdom / obviously correct but I just don't understand how the actual agitation (vs water flow itself) can make much difference.

It's a good question. And one that has plagued me in the past!! I am not quite sure that I have fully worked it out (certainly not scientifically!) but this is where I landed.

• Agitation increases the surface area of the water exposed to the air, increasing the water's ability to absorb oxygen above what a flat surface can.. (A flat surface does, but not as good as an agitated one).
• Flow is still required to ensure that oxygen is pushed around the aquarium, regardless.
• Oxygen is dependent on the aquarium environment and the amount of life that places demands on it. (1 guppy in a 50G = low DO demand, versus 50 Angels in a 50G = higher DO demand)
• Aquascapers generally have a high plant mass to low fish stock, meaning that a) plants create good amounts of net oxygen provision, and b) there is not much oxygen demand from other life.

Where I think I ended up on this was that the typical aquascaping environment (not so many fish, lots of plants) means that surface agitation becomes less important to support life. But move to a tank with over-stocking of fish, then you are going to need to maximise the oxygen intake, in which surface agitation is one method. And this is why I think you see videos of aquascapers with beautiful aquairums and a near-flat surface. e.g. I don't think you could do that in a bare and overstocked cichlid tank.

Well, that's where I ended up anyway! The topic was enough to drive me nuts and by a Disolved Oxygen probe and waste weeks testing it! 😀

 

[Yugang]

The physics of gas transport and gas exchange between air and water can become quite complex when details matter or on less controlled situation than aquarium. Example in case CO2 absorption in oceans, as studied for climate change, and how it depends on sea waves and other conditions.

For our tank we can greatly simplify the answer, to what are the two main factors:

• You don't want your surface to be stagnant, as in that case gas transport will be limited by diffusion in the boundary layer between water and air and be much reduced. Always have at least a reasonable flow at the aquarium surface.
• You want to avoid that a nearly stagnant water column gets covered by some layer of oily organic substances that would reduce the transport and effective 'breathing' area for gases. Surface agitation helps, but alternatively also skimmers or airstones.

The intensity of surface agitation matters less than is often assumed in the hobby, and it is also a misunderstanding that the small waves in an aquarium increase surface area or gas exchange significantly.

In summary, as long as there is some surface agitation, not stagnant, and the surface is clean, from the perspective of gas exchange it does not make a significant difference how much agitation we have in an aquarium environment.

 

[Bradders]

In summary, as long as there is some surface agitation, not stagnant, and the surface is clean, from the perspective of gas exchange it does not make a significant difference how much agitation we have in an aquarium environment.

I think that is a good summary, especially the clean surface point. If you have a CO2-injected aquarium with a surface skimmer, and stop that surface skimmer once equilibrium is reached, then you will observe the pH dropping further as that gas exchange becomes harder through the unclean surface. Conversely, if you have a skimmer running overnight and that stops/fails, you will find that the CO2 does not off-gass as much as you would with a surface skimmer operating. e.g. a return to a pH of 7.7 becomes a return to a pH of 7.5, indicating there is more CO2 remaining in the water. Over the last few years, I have found a surface skimmer to be a very useful part of the aquarium environment. (I started with much suspicion about their relevance when I started the high-tech journey in 2023!).

I think the other point I want to (somewhat boringly) labour is that fish size matters. For example, a 4-inch fish demands much more oxygen than a 2-inch fish. It's not twice the amount, but closer to 5 times the amount. It's not that linear, according to research I have read, but it's certainly not 'double the fish size, and you need only double the DO' - it's more.

 

[Bill the fish]

In my basic and somewhat primitive mind I think that the scummy protein build up on the surface pretty much must reduce oxygen transfer from the air to the water. So when I asked about this on You Tube many folks suggest that even on unfiltered tanks some sort of circ pump should be used just to help preven the scum build up and reduce dead spots in the tank.

 

[BarrWarr]

Thanks for all the comments. I think I'll have to pop the spray bar back on then to create some surface agitation, even on the lowest setting and pointing at the glass behind it, it's still a bit much for the Betta (and the frogbit). I did try just having the duck bill attachment on the outflow, pointing it into some hardscape and that suited the livestock but not the surface agitation.

Not really sure what the answer is tbh!

 

[BarrWarr]

What kind of outflow do you have?, I also have a betta and small fish but things seem fine with my glass lily spin outflow.

This is my current outflow now I've popped the spray bar back on. I did just have the elbow piece pointing at the rocks but this created no surface agitation.

I've no clue about lily pipes or if they'd work on my filter/setup?

 

[Yugang]

Thanks for all the comments. I think I'll have to pop the spray bar back on then to create some surface agitation, even on the lowest setting and pointing at the glass behind it, it's still a bit much for the Betta (and the frogbit). I did try just having the duck bill attachment on the outflow, pointing it into some hardscape and that suited the livestock but not the surface agitation.

Not really sure what the answer is tbh!

As @Andy Pierce said before surface agitation is overrated. It is mostly discussed for high tech tanks, but that's not relevant for your question. If you are worried about gas exchange in your low tech tank, perhaps you shouldn't, then a simple and cheap skimmer might be a pragmatic step. A clean water surface may already be enough, even with very little water movement in a low tech tank.

 

[BarrWarr]

As @Andy Pierce said before surface agitation is overrated. It is mostly discussed for high tech tanks, but that's not relevant for your question. If you are worried about gas exchange in your low tech tank, perhaps you shouldn't, then a simple and cheap skimmer might be a pragmatic step. A clean water surface may already be enough, even with very little water movement in a low tech tank.

Thanks. Without taking things out, I wouldn't be able to fit a skimmer in. Now I've put the spray bar back on, the Ember tetras are now swimming close to it, into the flow!

 

[BarrWarr]

Just been going through the same challenge! New tiny fish meant my Biomaster 850 was too powerful with a certain lily pipe intake. (It has huge amounts of slits). Just swapped to a Chihiros which has under half the slits and slows the flow. I could have done this on the oase, but hey, it's just another reason for me to fiddle around with stuff. 🙂

Now, some genius told me about the Betta challenges in fairly low plant mass tanks. If you are a little worried, you can shoot the outlet water down a pipe, whilst the airstone counteracts that with an upflow of bubbles in the same pipe. This causes a lot of turbulence and oxygenation, but does not result in a lot of flow. Can't say that I have done this personally, but it sounds like a plausible solution to the 'oxygenate but with limited flow' challenge.

Thanks. Im not entirely sure what you mean re what the genius told you - I can't picture what it means by 'shoot the outlet water down a pipe, whilst the airstone counteracts that with an upflow of bubbles in the same pipe'?

Im probably just been stupid but this sounds a possibility worth exploring.

 

[Bradders]

Im probably just been stupid but this sounds a possibility worth exploring.

Not stupid at all, just my lame explanation!

1. Purchase of a see-through tube that is wider than the pipework coming out of the filter, and also enough to fit an airstone in.
2. The pipe is inserted into the substrate, with the airstone fed into the bottom of the pipe and lying on the bottom to force air up the tube.
3. The outlet from the filter is plumbed into the top of the pipe, so the outflow goes down the tube.
4. The force from the flow + the force from the airstone creates a lot of turbulence, but does not create a lot of flow in the tank.

Now, I have never done this myself, but it sounds plausible in the design!

 

[BarrWarr]

Thanks. I've been having a tinker and think I may have come up with a solution. I cut a filter sponge in half and placed it in between the spraybar and the glass. I then turned the spraybar in small increments so that just the right amount could 'escape'. This has allowed me to run the outflow at full speed and create a bit of surface agitation/circulation. I attach a pic and a link to a video (which i hope works) - does this amount of agitation seem adequate?

 

[Bradders]

That looks fine to me. Nice little baffling of the output!

 

[BarrWarr]

That looks fine to me. Nice little baffling of the output!

Great, thanks! I had a couple of unused Poret sponges from Envobee Shrimp so once cut in half, due to it being hollow centrally, it kind of wraps around the spraybar nicely. It doesn't look too silly either really.

 

[GaryJ]

Another solution for adequate water exchange without excessive flow is to oxygenate outside of the tank. Depends what type of filter you have but running an airstone and pump through filter media or between the filter and tank input provides full flexibility for gas exchange. eg if you have a canister filter a home made K1 media filter in a cheap plastic container and air pump isn't difficult. With a sump it's very easy. I also use a small UV light in one of them which is set up between the output and filter so beneficial bacteria are not compromised. Another possibility is to build a weir at one end which also keeps water surface clean.