How much flow is too much?

[NC AL]

So how much flow do you guys recommend? I know this question can have varied responses. Internet searches seem to say around 6 times turnover rate. However other discussions talk about how important flow is for spreading nutrients, detritus removal, etc. 6x just seems awfully low.

Would 10x be too hard on plants? Or nano fish?

 

[Naturescapes_Rocco]

10x has always been my understanding for turnover in most high-tech tanks.

https://www.instagram.com/isaak_aqua/

This guy has a massive hillstream tank with CO2 injection that has closer to 20-50x turnover every hour or more, so it's all "how long is a piece of string".

My bowl has zero flow/turnover, just to make things even more complicated!

 

[Kwyet]

You want enough for gentle movement throughout the tank and to handle the bioload of your fish. In small bowls, the inhabitants and plants can take care of that. In larger tanks, I’m sure it varies with the type of scape, density of planting, and choice of fish.

 

[GreggZ]

Flow is often misunderstood.

People hear you need good flow and they put in loads of power heads and plants are waving around frantically. That is not good flow.

IMO what works best is a wide laminar flow. With a purpose.

In my tank that's flow across the top of the tank, down the front glass, then across the substrate to the back of the tank.

And it's hard to judge strictly by turnover rate. It also as to do with how it's applied. For instance spray bars create a nice wide flow. Pushing the same amount of water through a single narrow outlet can create a LOT of turbulence. Which some plants just don't like.

And even with spray bars the size of the holes makes a difference. I generally drill mine out so they are larger holes so they have less velocity.

In my tank I have about 13x, but it's distributed pretty gently. And in reality I could probably get by with a lot less.

 

[Unexpected]

My tanks seems to do best when every plant has a bit of movement.

 

[Mr.Shenanagins]

And it's hard to judge strictly by turnover rate. It also as to do with how it's applied. For instance spray bars create a nice wide flow. Pushing the same amount of water through a single narrow outlet can create a LOT of turbulence. Which some plants just don't like.

Couldn’t agree more. IME experience plants that get blasted with heavy currents become algae magnets.

 

[NC AL]

Thanks for everyone's input. My return pump is only set around 30% (approx. 8x), so I will be turning that up. My return nozzle has 2 loc-line outlets. I currently have 1 directed towards the surface for agitation and the second towards the lower side in hopes it creates a circling current around the bottom to help reduce detritus build up. My tank it too small for a separate powerhead. So the return output is all I have to work with.

 

[Koan]

in hopes it creates a circling current around the bottom

The turnover-per-hour figure is an old rule of thumb that get used to get used for fish-only aquariums. The point was to give an idea how many times water was circulating through the filter media, or through the sump / skimmer etc, to keep all the ammonia metabolized

In a planted tank you are looking for the circulation pattern that adequately distributes CO2 to all your plants Just watch to see that you can see plant motion in the corners and odd spots

 

[BranchScape]

I think GreggZ nailed the answer on general flow rates, so hopefully this stays on topic as a related follow‑up question on flow.

Can we talk about inflow and outflow positioning?

I’m replacing my filter with an Aquael Hypermax 4500 BT on my 120P, which has two inlets and two outlets, and I’d love some input on the best layout. Currently, I have the inlet in the far left corner and the outlet lily pipe in the front left corner.

Should I double them up on one side, or place one inlet and outlet on the far right corner? Alternatively, would it make sense to double up the inlets and split the outlets as described above? I’m having a hard time deciding what’s optimal.

If this were an empty tank, I’d test with dye, but it’s a four‑month‑old, maturing scape, so that’s not really an option.