High flow VS low flow returns

[kpiotrowski]

I am a high flow kind of guy and so I am providing an example of why. first off please feel free to confirm the math...at which point I would have a mute point.

this is an example for a 300g tank flowing 1000gph return (which would be minimum for me)

all measurements rounded
lets take my tank, 300g ( outside dimensions, but irrelevant)
72 inches long ( actual internal) = 183cm


flowing 1000gph return over a coast-to-coast overflow

1000gph = 3785412 cc per hour
=63090 cc per minute
=1051 cc per second

1051cc per second over a 183cm span = 5.75cc per second per cm

so, if my math is correct then it can be said that flowing 1000gph over a coast-coast on a 6 foot tank, then for each cm you are only dumping little more than a tsp. of water over the overflow each second. that is only the VERY surface of that water and would not include much in the way of heavier detritus.

Seems my math must be wrong...or this is some food for thought and arguement for higher return flows.

 

[Peppie]

Lets throw the math out of the window for a min.
If I have an overflow and I am pumping 1000 gph over it, and lets say the depth of the water that is going over the edge of the overflow is 1/4'' high.
Now I back down the gph that is running over the edge... lets say to 400 gph. Now the depth of the water going over the edge is 1/8''.

Now I have cut the depth in half. Am I get enough of the suspend poop and crude out of the DT???

It seems as though you would get twice as much crap out of the DT at the higher flow rate... Yea???? NO??????

 

[kpiotrowski]

Lets throw the math out of the window for a min.
If I have an overflow and I am pumping 1000 gph over it, and lets say the depth of the water that is going over the edge of the overflow is 1/4'' high.
Now I back down the gph that is running over the edge... lets say to 400 gph. Now the depth of the water going over the edge is 1/8''.

Now I have cut the depth in half. Am I get enough of the suspend poop and crude out of the DT???

It seems as though you would get twice as much crap out of the DT at the higher flow rate... Yea???? NO??????

you said you cut the flow in half...from 1000 to 400? so thats 60% drop.

but yeah, I will bite. if you double the the flow you will get twice as much DT water out of the DT in any given amount of time.

 

[Peppie]

What do you want to export out of the DT????

POOP????

or


Protein ????

I would like to get both. So do I divide my overflow in half??? One half with tall teeth, and the other half with short teeth???

 

[kpiotrowski]

What do you want to export out of the DT????

POOP????

or


Protein ????

I would like to get both. So do I divide my overflow in half??? One half with tall teeth, and the other half with short teeth???

this is the debate peppie and I have about the difference between a coast-to-coast toothless overflow and more common shorter toothed oveflow. When considering what size particles will be travleling out of your DT my opinion is with the same amount of return flow a coast-to-coast overflow skims the water surface, and a shorter overlfow with be taking in water at a much deeper level allowing heavier suspended particle to travel through.

 

[Spinner]

So if i understand what your saying" women with no teeth are sexy" and the one's with just two large front teeth stay away from......it this what your saying?

 

[user 26995]

So if i understand what your saying" women with no teeth are sexy" and the one's with just two large front teeth stay away from......it this what your saying?

LOL...wait!...WHAT?

 

[user 26995]

I dont get what the size of the teeth have to do with it? The higher flow, the higher the water level over the overflow regardless of the size of the teeth. The actual flow in the tank is going to determin how much detritus and such actually flows out of the overflow.
Even at the lower return flow, if the flow in the tank is enough to keep the detritus in suspension and moving to the surface, it will travel out the overflow.

 

[mfinn]

The actual flow in the tank is going to determin how much detritus and such actually flows out of the overflow.
Even at the lower return flow, if the flow in the tank is enough to keep the detritus in suspension and moving to the surface, it will travel out the overflow.

I've always thought the same.

 

[kpiotrowski]

So if i understand what your saying" women with no teeth are sexy" and the one's with just two large front teeth stay away from......it this what your saying?

Have you been drinking....or :hippie:

 

[Spinner]

:hippie:wh..whey would you think that......i will be removing my systems teeth before fire up and may add some egg crate installed on the back side. Will see whats needed then so no teeth gets my vote for high flow.

 

[user 26995]

The big reason for teeth on the overflow, is to keep snails and other critters and small fish from getting into the overflow. I dont think you really want to go toothless!

 

[Peppie]

IMO the teeth will restrict the total surface area skimmed from the tank by 50% depending on the spacing of the teeth.
If you are worried about critters taking a ride place screens on the plumbing.

BTW I have HEARD that if you have gone toothless, you'll never go back!!

 

[user 26995]

I dont know...I would think that the screen on the plumbing would get clogged too easy. That would cause the tank to overflow, if the water volume in the sump return is more than the available space in the tank.

 

[kpiotrowski]

Ok lets get away from teeth for a bit. and let forget about coast-to-coast overflow. The simplest way I can think of to make my point is....and first of all YES the right flow in the DT to keep things in suspension is the first consideration. but what my query is the size of the wall of water that flows over the overflow box. does it make sence that a wall of water that is 1 inch high will catch more heavier suspended detritus than a wall of water only 1/32 of an inch? lets start there. and if that makes sence to anyone then how do you make that higher wall of water? more flow right?


now, the length of the overflow has everything to do with this too right. 1000gph flowing over a 12inch edge will be higher than a 48in edge. so, if any of the above is a consideration then there must be and ideal size of oveflow edge compared to return volume.

just saying, I see it all time...and you do too, heavier chunks are exiting the tank right over the overflow box an inch or even half inch below the waters surface. so if you cut that flow down, or increase the size of overflow box ( coast to coast) and end up with a very thin sheet of water that is exiting the tank, are you missing any of those larger particle and is it benifitial to get them out sooner?

these larger partical could be food for example, and an argument may be that yes you want them to stay in the tank so this fish have a chance to eat them. this would be a prefernce based on your sytem. but if the above has truth to it, then it has truth to it and perhaps its subject to explore is my point of this post. Not trying to be right. Just trying to explore.

 

[user 26995]

Well I for one, think everything you said is correct.

 

[kpiotrowski]

BTW I have HEARD that if you have gone toothless, you'll never go back!![/QUOTE]

Now here is another one I'm trying not to read in to!

 

[Herefishyfishy]

Ok lets get away from teeth for a bit . . . Just trying to explore.

Very good writing my friend. I am a fan of the largest flow through the sump as possible, balanced against the least power and heat consumption. The concept of sump water needing more time to be skimmed goes against basic physics. Why have the sump water squeeky clean and the display full of polution. Get the water to the skimmer, it will pull as much as it can regardless. Get the detritus out and one will be amazed how easy to keep nitrates down. How little I change my water is a highly protected secret, but why I have a huge skimmer and other water purification systems is clearly not.

 

[kpiotrowski]

Very good writing my friend. I am a fan of the largest flow through the sump as possible, balanced against the least power and heat consumption. The concept of sump water needing more time to be skimmed goes against basic physics. Why have the sump water squeeky clean and the display full of polution. Get the water to the skimmer, it will pull as much as it can regardless. Get the detritus out and one will be amazed how easy to keep nitrates down. How little I change my water is a highly protected secret, but why I have a huge skimmer and other water purification systems is clearly not.

Thanks mike. and thanks for taking this thread to an adjacent point! could'nt have said it better myself. Get that skimmer as dirty of water as you can. as far as what your skimmer gph is rated for that is only the physics of the skimmer with contact and dwell etc....soooooo, skimmer gph has NOTHING to do with return gph. return gph has ONLY to do with the size of the display and how much of that display water do you want to get out of there and down to be processed.

I would really like the time to do an experiment with same tanks and pumps but different lenght oveflows, dump in somethings into the display that are color coded with differnt weights, run the overlfow through some floss and see what gets skimmed and when. of course there are many more variables, but that would be a start.

 

[dnjan]

Please remember that it is FPS and not CFM (or GPM) that keeps detritus in suspension.

Or, without the abbreviations, it is velocity (feet per second) and not flow (cubic feet per minute or gallons per minute) that keeps detritus suspended.

So as long as the thickness of the flow layer is larger than the suspended particle (you can't move 2-mm diameter Urchin pellets over a toothless coast-to-coast if the flow is only 0.5mm deep), you need to compare the water velocities going over the overflow to determine which one would be more effective for detritus.

So convert the flow to CFM (about 7.5 gallons per cubic foot), and divide by the overflow area (length times depth of each section or "tooth space" times the number of tooth-spaces) to get velocity.