Flow, Aeration and Fish

[Bradders]

Hi All,

I have a small 100L Aquarium—a moderate amount of plants and about 20 small 1-2 inch fish. Filtration provided by 2 x Oase 250 Biomasters. (Redundancy and maturing for the next tank!) No CO2 injection, so it's all Low-Tech. Each Biomaster (with my head height) produces around 500L per hour of flow. (I am not sure whether it's 1000L of flow or 2 x 500L of flow, as I am sure there is a difference between one unit providing 1000L versus two units each producing 500L!).

I am constantly messing around with the outflows of both filters. I want to create good.flow through the tank, but I am also conscious that the small fish are getting blown around a lot.

The problems I have are either:

1. Lots of water flow through the aquarium, but the fish seemed overwhelmed.
2. Little flow through the aquarium (e.g. baffled output, reduced output or pointed at the back wall), and the fish seem happier, but there is not a lot of movement of the plants.
3. A mixture of the above, but trying to add air gas exchange by breaking the surface with the outflow AND balance the flow through the aquarium,

So, I thought I would ask the community (of fish and planted aquariums) on how they would best deal with the above issues to create a good equilibrium. I understand flow for plants is very important, but maybe not so important for fish, so how do you balance this puzzle?

Any ideas on the above would be greatly appreciated!

Brad

 

[AlecF]

This, always this. I have a Fluval 307 on a 100 litre shallow tank, with, stupidly, a dozen embers, who really don't like flow. Spraybars definitely seem the obvious method to run the water in. If I put them along the back then there's a wash that doesn't direct towards the filter pipe, so I have them at the side, but it's a long way to push the flow, and if the output is too high I risk making the embers miserable. Then there's floating plants: does one really want them all forced to one end? I have 2 sponge filters to help add oxygen, but the pipes are so long and the tank so (relatively) low, that the bubbles are soon at the surface. I wonder about reducing the size of those air pipes. I have a slightly unusual tank, with euro style braces and I tend to direct the flow to baffle off those, so that it isn't full force. It's impossible to use the full force of a 307 on a tank of this size as far as I can see. I've never tried directing the flow downwards as it's hard not to feel it's too powerful for the small fish, and reducing the flow too much risks damaging the filter. Without the embers I'd be much less aware of the problem. So, I'm interested to see replies.

 

[castle]

When I add a filter to a pre-running tank to season, I normally clamp the incoming tube to the top and run the inflow into a sponge this reduces the flow considerably. It will make some noise, but the surface agitation is great for bringing in oxygen. I did this a few months ago; It’s running now, I’ll take a photo.

i am not a planted tank keeper; so flow has always been something I struggled with. Tanks always have dead spots and places for detritus to collect; I think this is why I do somewhat well with ripariums 😅 I also don’t keep high flow fish.

My priority in aquariums is to have have an ample amount of oxygen, and I do this by agitation - I’m trying to make sure I am always covering the biochemical oxygen demand of bacteria, I think this is fundamental to a “nature” aquarium. I guess this means I always have stable atmospheric co2 too 👍

 

[_Maq_]

I don't use filters, only internal pumps for water movement & oxygenation. I have two 100 liter tanks, both are served with AquaEl 500 Circulator (meaning 500 L per hour) with venturi. The flow is satisfactory for plants, and not too strong for fish. Admittedly, my tanks' shapes are almost exactly a cube.

 

[ElleDee]

Are you using the outflows that came with the canisters? This seems like the kind of thing spray bars are for.

 

[Bradders]

Are you using the outflows that came with the canisters? This seems like the kind of thing spray bars are for.

At the moment, I am using one spray bar (on canister 1) and the standard nozzle (on canister 2). Even the spray bars can be quite powerful.

Now, I can reduce the flow on each canister by 50% (each one at 250L per hour instead of 500L per hour), but then I am halving the turnover through the canisters.

I am constantly caught between the flow in the tank and the flow through the canister!

 

[ElleDee]

At the moment, I am using one spray bar (on canister 1) and the standard nozzle (on canister 2). Even the spray bars can be quite powerful.

Now, I can reduce the flow on each canister by 50% (each one at 250L per hour instead of 500L per hour), but then I am halving the turnover through the canisters.

I am constantly caught between the flow in the tank and the flow through the canister!

Can you get a longer spray bar to distribute the force more? I am more of the mind that adequate flow distribution and surface agitation is more important than hitting a high flow rate anyway, though that may be a bit heretical around here.

 

[Bradders]

Can you get a longer spray bar to distribute the force more? I am more of the mind that adequate flow distribution and surface agitation is more important than hitting a high flow rate anyway, though that may be a bit heretical around here.

I think I'll have to do some cutting; one spray bay is not long enough, and two spray bars are too long for the tank! (The bracing bars are also very restrictive). However, I agree that I will have to compromise at some point, but I am not keen on restricting the filter output. I think! 🤪

I certainly do have a lot of surface agitation at the moment - but again, will this gas exchange (turbulent surface agitation) release too much of the precious C02 in my Low-Tech aquarium?!

 

[ElleDee]

I certainly do have a lot of surface agitation at the moment - but again, will this gas exchange (turbulent surface agitation) release too much of the precious C02 in my Low-Tech aquarium?!

You know, I had this concern too at one point, but I read so many conflicting things about it I decided to ignore it. Fast forward a few years and I have run low tech tanks with a sponge filter, a HOB, and a slightly oversized canister filter with a spray bar, all with very different rates of flow and surface agitation, and all of them have a measurable pH drops during the dark period, suggesting that CO2 from respiration is building up to higher-than-atmospheric levels. I still don't understand all the factors at play, but at any rate I don't think it's really causing me a problem. These tanks have been running consistently for between 1.5 and 4 years with no major disturbances, so there's been lots of time for the microbial communities to establish.

 

[_Maq_]

I will have to compromise at some point, but I am not keen on restricting the filter output.

If you notice my signature, you'll know my opinion. In modestly stocked planted tanks, any artificial bio-filtration is very likely redundant. And if you keep it? As long as there's any flow in the filter, some microbes will be there doing their jobs. A problem may occur at the moment of sudden change. If you decrease the flow, you supposedly decrease also oxygenation of your filter, and the microbial community within will have to adapt to new conditions. But later on, you'll be safe.

will this gas exchange (turbulent surface agitation) release too much of the precious C02 in my Low-Tech aquarium?!

Or the contrary? Will surface agitation ADD precious CO2 in the time of need? Actually, surface agitation is a way to maintain some level of CO2 permanently in the water column. I'm practicing this for years and plants do not complain. Neither do I because relatively slow growth fits my intentions.

suggesting that CO2 from respiration is building up to higher-than-atmospheric levels.

Microbial respiration increases CO2 content above air-equilibrium almost inevitably. In addition, most of that CO2 is produced in the sediment and relatively slowly diffuses into water column. And let's not underestimate plants' abilities in gathering CO2 through their roots. This ability was detected in some species (Isoetids) quite a while ago. Since then, scientists revealed that this ability is far from restricted to a handful of species and is probably very common.

 

[hax47]

Or the contrary? Will surface agitation ADD precious CO2 in the time of need? Actually, surface agitation is a way to maintain some level of CO2 permanently in the water column. I'm practicing this for years and plants do not complain. Neither do I because relatively slow growth fits my intentions.

I have not been able to go below the air-equilibrium CO2 levels in my aquariums, I suppose that would need a decent plant mass and strong lighting. My room-air-CO2/water equilibrium is reached between 1.4 - 1.8 ppm, but to go that low, I need to aerate the aquarium water heavily for some time in a small jar with an airstone. Usually, the CO2 levels in my tanks when no CO2 was added were between 2 and 4 ppm. To add CO2 from the air, one would need really low aquarium CO2 levels (below 1.4, or whatever the actual equilibrium is), and even then, because of the small air/water difference, the diffusion from the air would be quite slow.

I certainly do have a lot of surface agitation at the moment - but again, will this gas exchange (turbulent surface agitation) release too much of the precious C02 in my Low-Tech aquarium?!

In theory, it is not too difficult to test if the increased agitation leads to CO2 release - you can take an aquarium water sample in a jar, aerate it with an airstone for a few hours, and compare the pH with the aquarium pH - if higher in the jar, you remove CO2 with increased aeration, if smaller, you add CO2 from the air; I would be surprised if the latter happened.

 

[JohnCooke]

There is another perspective.

Do you really need as much flow as you think you do?

Planted tanks did very well for many years with sufficient surface flow to stop excessive CO2 build-up at night. Excessive, that is, for the fish. I note an emphasis on increased flow in planted tanks on several forums over the immediate past. I can understand it for hillsteam biotopes, but is increasing flow always what we should be striving for?

Consider your canister filters, for example. I suspect that it's the filter volume inside them, rather than the speed of the water movement, that's [mostly] the key to their success in filtering your tank. Why not dial them back a bit and see what happens? If you're worried about detritus accumulation in the tank, well, the plants might welcome it, and it could be dealt with when you do water changes?

 

[tam]

1. Little flow through the aquarium (e.g. baffled output, reduced output or pointed at the back wall), and the fish seem happier, but there is not a lot of movement of the plants.

When you tried this, other than the plants not waving, what issues did you observe?

 

[Bradders]

When you tried this, other than the plants not waving, what issues did you observe?

It looked like waste was not getting pushed around and more suspended in the water column.

 

[OllieTY]

This, always this. I have a Fluval 307 on a 100 litre shallow tank, with, stupidly, a dozen embers, who really don't like flow. Spraybars definitely seem the obvious method to run the water in. If I put them along the back then there's a wash that doesn't direct towards the filter pipe, so I have them at the side, but it's a long way to push the flow, and if the output is too high I risk making the embers miserable. Then there's floating plants: does one really want them all forced to one end? I have 2 sponge filters to help add oxygen, but the pipes are so long and the tank so (relatively) low, that the bubbles are soon at the surface. I wonder about reducing the size of those air pipes. I have a slightly unusual tank, with euro style braces and I tend to direct the flow to baffle off those, so that it isn't full force. It's impossible to use the full force of a 307 on a tank of this size as far as I can see. I've never tried directing the flow downwards as it's hard not to feel it's too powerful for the small fish, and reducing the flow too much risks damaging the filter. Without the embers I'd be much less aware of the problem. So, I'm interested to see replies.

Zip tie an intake sponge over the nozzle that comes with the Fluval 07s, then the water just diffuses into the tank far more gently

 

[Zeus.]

Having had a 500l litre tank with a Fluval FX6 and twin Maxspect Gyres the output to tank volume ratio when maxed out was about x36, which is far in excess of whats needed. However only had the gyres maxed out for short periods as the Gyres came with a controller which gave 24 timed schedules for gyre settings. The fish all small with the largest no bigger than an ammano had no issues when gyres was running on high settings. Although it was only for short periods of high tank turnover, during the non CO2/photoperiod one gyres was off whilst other was on low setting to allow for clean up crew to do their job. Worked well IME. Highish turnover for CO2/photoperiod with hourly 5 min boost turnover and low setting for twilight viewing/lights off, ever changing tank throughout the day
On side note the gyres didn't needed cleaning often at all.

 

[Onoma1]

My experience has been my 'higher energy' tanks need high flow. In these tanks I have focused on building the biomass quickly then dialing it down (Co2 and flow). Fish are only really introduced after I have started dualing down. In my medium energy or low energy tanks flow in terms of velocity of water within the tank is relatively unimportant. Atm I am trying to find ways of reducing it to zero by using emergent plants to naturally filter the water. Its more about balance and taking it slowly to reach a point of equilibrium and not worrying about the bumps along the way. I would add that I try to match the fish to the environment. Hope this helps!

 

[Bradders]

My experience has been my 'higher energy' tanks need high flow. In these tanks I have focused on building the biomass quickly then dialing it down (Co2 and flow). Fish are only really introduced after I have started dualing down. In my medium energy or low energy tanks flow in terms of velocity of water within the tank is relatively unimportant. Atm I am trying to find ways of reducing it to zero by using emergent plants to naturally filter the water. Its more about balance and taking it slowly to reach a point of equilibrium and not worrying about the bumps along the way. I would add that I try to match the fish to the environment. Hope this helps!

Let me know how "Project Zero" goes. Sounds interesting!

 

[_Maq_]

my 'higher energy' tanks need high flow

In my medium energy or low energy tanks flow in terms of velocity of water within the tank is relatively unimportant.

Interesting observation. I can see certain logic in it. In hi-tech, there are steeper gradients of gasses and nutrients at phase interfaces and flow may increase diffusion in diffusion boundary layers. Still, I consider mass flow always beneficial thanks mainly distribution of oxygen.

 

[Bradders]

Consider your canister filters, for example. I suspect that it's the filter volume inside them, rather than the speed of the water movement, that's [mostly] the key to their success in filtering your tank. Why not dial them back a bit and see what happens?

This is something I am leaning toward. I don’t think doubling the flow through a canister creates a 2x better filter, or doubling of load capability. In short, flow through a filter is not as critical as the biological surface area available. My Oase 250 turnover really does not get much above 450 to 550 litres per hour, so only getting 4 /5x turnover in my aquarium. However, fish are healthy and water is very clear.

But as you look at plants, there seems to be more opinion on higher flow (flow is king) and 4x starts to look a bit paltry. Yes, I agree that you need to experiment but I am always keen to understand the principle and “sum of the parts”.