Flow in Aquarium. What is right...

OK I did it, I have created a thread about what is the right flow in an aquarium

TLDR; How do I know I have the right level of flow in my tank

I have been having a few issues (possibly just in my head) about flow around my new tank.



My setup is a 180l (~47 US gallon) tank with an Eheim 2217 canister filter (rated at 264 GPH) which was originally setup with a small spray bar across the back of the tank in the corner opposite the intake which gave me flow which looks fine from the side:


but not so good in the rest of the tank without the spray bar.



The flow here was very low (no movement on plant leaves and not much movement towards the filter intake)

Video of flow (or lack of it)

So I got an extension for the spray bar to make it go most of the way across the tank but the flow was then really poor

and this was not actually making the water hit the glass on the opposite side so whilst there was a little surface agitation across the tank, there was very little flow under the surface.

So the other day I added a Newa Wave 1.6 Adj circulation pump (800 l/h => 1,600 l/h) and set on the lowest setting this caused quite a bit of current under the surface (in fact it uprooted the amazon sword it is in the middle of)

I also cleaned the filter today and made a few tweaks with pipework and media to increase the flow

or with a longer spray bar

But I keep coming back to the physics of this and if the spray bar is creating the circular flow above then the circulation pump is then conflicting with this and I guess to some extent creating a vortex.

I have had lots of advice about adding new pumps, creating new flow bars etc. but no real idea of what it is I am aiming for.

My understanding is that I need water movement for a few things

• Surface Agitation - This will enable gas exchange
• Current - To distribute nutrients to plants and and ensure the detritus is moved towards the filter intake

So after all this rambling, I am looking for ideas as to what flow I should be aiming for (not what kit I should add nor how I should change what I have). There is quite a bit about flow in a reef tank but very little about what it should look like (in practice anyway) in a freshwater setup.

eg. you have things like which talk about flow patterns but not about how you might actually put them into place (particularly with items in the tank which obviously affect flow)

Can anyone suggest the best flow pattern for my tank (might be my simple mind but pictures are always more helpful than words :cool. Also how can I tell whether my flow is actually good (ie. is healthy for the plants, fish and tank)

 

Well, it really depends on the kind of biome you are looking at creating, the amount of nutrients and waste, the plants and fishes needs, and more, I'm not an expert or anything, and I'm pretty new to the hobby myself, but aquatic ecosystems are something I've been studying and coming to understand for as long as I could read, so I might be able to help you out a bit, one possiblity is to create an underwater current straight across the tank where the current is generated at a point just below the surface as well as towards the bottom of the aquarium, and have the water re enter the filtration system on the opposite side of the aquarium, which would give you the greatest ability to control flow level and current strength, another option is to generate a circular current across the tank, like the original current you saw from the side of your aquarium, but this can be problematic and leave slack areas where detritus can collect, specifically around large decorations, as far as telling if your current is good, it really depends on the biome you are trying to create, but you should be able to see your plants wave in moderate to low current, or to see flake food, or waste matter flow with the current, areas of low to no current can be okay in an aquarium so long as you make sure to clean regularly, sorry I didn't add any pictures to help explain, I'm relatively new to the forum and don't really know how to do that yet, but I do hope I've helped you out a little bit.

 

OK not much input which suggests this is difficult to determine but everyone must have played with their flow.

Lots of things seem to suggest that front to back laminar flow like the first diagram in the first post is good across the whole tank. This seems sensible in terms of distributing nutrients etc and avoiding dead spots.

But I am also seeing that flow across the length of the tank could be good to blow detritus to the intake and also to ensure that the turnover of water is higher (not the same water being cycled through the filter). This however is contradictory to the the flow above...

Even if it is just issues and experience you have with flow I would really like some input...

 

You want flow to happen throughout most of the tank. However places that are missed will still filter due to the fact that water tries to get into equilibrium. So dissolved particles within the water move from high concentration to low. For detritus and larger particles the water flow to keep it moving might be so high your fish struggle.

 

Exactly

 

Does planting come into this though? Since I have added a circulation pump and can see plants swaying I have noticed a big improvement in those plants on the opposite side to the spray bar and ones that were just existing are now growing.

Also nitrates have dropped (not sure if this is due to increased plant growth or more detritus making it to the filter quickly)

The same fundamental question arises though in what flow do others have in their tank. I would be interested to see how others have their tanks setup and what sort of flow / surface agitation they have.

 

Probably due to both on nitrates. However the better plants could be due to circulation because it is getting more CO2 for them to "breathe"

 

Yes, plants, just like any other decor or aqua scaping does play a role in necessity of flow strength as well as the pattern of the flow, plus many plants highly appreciate a bit of flow in their natural habitat as it brings them nutrients and pulls away their waste, as does any other living thing, it's harder to grow when trapped in your own waste. The nitrates are likely dropping in part because they are more accessible to the plants as well as the waste being more frequently taken in by the filter, and the water movement also helps with gas exchange, as far as my flow, I have a tetra ten gallon tank kit which I acquired a little over a month ago, there is a bubble bar and a filter both on the same side creating a simple circular current, with a few areas of reduction due to planting, the back to front surface current seems to be the most common set up in home aquariums from what I've seen so far.

 

Bumping this as would be really interested to see others flow setups; particularly in similar size (~47 us g) tanks that are planted