River Tank - Flow Discussion - The Planted Tank Forum
 
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post #1 of 13 (permalink) Old 06-17-2017, 03:00 PM Thread Starter
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River Tank - Flow Discussion

Hi Folks,

So this is basically a duplicate from an entry in my river tank journal, but I figure I will get more responses here. I'm looking for input/pro's/con's and other suggestions on how to best create a river like flow in my project tank, a 265 gallon, 7' long tank. The design is going to come down to this plan, or an overflow that i am going to be working on sketching out this afternoon. I have rejected an internal river manifold setup because, after looking around at powerheads, I won't be able to achieve the flow i need in this size of a tank. There is just too much water for that kind of setup.

So with that in mind, for your consideration, here is plan one!

--------------------------------------------



So this is some "high tech" graphics work in Microsoft Paint, so don't hold it against me. lol. What we are looking at here is the top down view on top, and then the side view below it.

The red baffle that would run most of the length, and the entire height. I didn't fill it in with solid color on the lower pic, but imagine that's an acrylic wall (or other material).

The green dotted lines on either end of the baffle would be either single or double lighting egg crate from Lowes/Home Depot. This would be for two reasons....first, to keep fish and most stuff out of the baffle area. 2nd is to help straighten the flow, so its more even. This is similar to how they control air in a wind tunnel.

I would like to put in 2 corner pieces (brown/tan) to sort of shape the flow and encourage the water turn a little bit. Maybe not necessary, but I think it will help efficiency.

The blue-gray pieces are a stand I would create to mount a pair of pumps. For pumps, in this plan, I am thinking about a pair of the Jaebo DCT series that have the speed controller. Then I would scheme up some nozzles to spread out the flow a bit, and send it down the backside of the baffle. Additionally (not pictured) I would use this space to hang the intake and outlet of a canister filter (or two).

Pro's:
  • Safer than an overflow system in terms of leaks and power loss.
  • Simpler to build
  • No tank drilling required
  • No sump (extra cost of a ~90 gallon tank) required, so more space available for storage in the stand. I have found this to be surprisingly important.
  • Variable flow for seasonal changes
  • No powerheads or pumps visible

Con's
  • Baffle area eats up real estate
  • I can't contour the rocks and gravel higher on one side, creating a pool on the other, as it would implead the flow.
  • Potential for fish/gunk to hide and/or decay behind the baffle.

Discussion Points
  • What am I missing? Surely there are some other con's with this plan!
  • Right now the river is at its seasonal low flow, of around 250 cfs at a specific measurement point. How do i go about converting that to a lower end of flow rate through the tank, and then adapt that to an appropriately sided pump? https://waterdata.usgs.gov/nwis/uv?p...gif_mult_sites
  • Because there is such a discrepancy between the size of the baffled area and the display portion, would i need to consider one or multiple recirc pumps along the right side of the tank? Or just running water at a higher velocity through the narrower section would be sufficient?

So what do you think? Do the pro's outweigh the cons? I'll post back here later this afternoon with the overflow design thats rattling around in my brain.

Here's a link back to the build thread: https://www.plantedtank.net/forums/12...k-265-gal.html


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post #2 of 13 (permalink) Old 06-17-2017, 04:28 PM
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Right now it looks like you are building a modified racetrack tank. From what i've seen there are 2 variations to them; One like what you've proposed (though normally the divider is in the middle of the tank), the other with some dividers that go most of the way across the tank, in several locations that the water is able to flow back and forth around (see poorly draw paint picture).

Flow could then be achieved easily with canister filters, or a dedicated closed loop pump (green circles in image), or a sump and return if you decide to go that route.

I have never built a tank like this, but I've seen them a lot of reefing forums for frag tanks where they are looking for an easier way to add consistant flow over large numbers of coral.

Pro's (we can keep all yours and add some at the bottom):
Safer than an overflow system in terms of leaks and power loss.
Simpler to build
No tank drilling required
No sump (extra cost of a ~90 gallon tank) required, so more space available for storage in the stand. I have found this to be surprisingly important.
Variable flow for seasonal changes
No powerheads or pumps visible
No equipment in tank option with inline diffusers and heaters
Easier intake and return prescreening options to keep plants/fish/snails/etc out of the pumps
more linear swimming distance for fish
twists and turns will allow for natural higher and lower flow areas similar to in a natural river system. Fish can choose what part they want to be in
baffle areas of consistant size means consitant flow (across the length of the tank) so you don't need higher velocity pumps

Con's
Baffle area eats up real estate
I can't contour the rocks and gravel higher on one side, creating a pool on the other, as it would implead the flow.
Potential for fish/gunk to hide and/or decay behind the baffle.
High and lower flow areas means there are likely to be "dead spots" where debris naturally collects
More tank surfaces to clean
seams on the front viewing panel (though being non structural you can minimize their appearance some)
requires more material for more dividers

additional discussion
I think you're looking at flow (volume) through the river incorrectly. You should look at it as time for an object to move "x" distance rather than time for "x volume of water" to be moved. in this case it will likely be (linear feet/minute) rather than (cubic feet/minute) if you tried to replicate the later you would literally have a river in your tank, rather than the much more realistic movement rate water within the river system.

Your fish are going to be much more concerned with how fast they are moving through the water (or the water is moving around them) than how much water volume they are swimming through.
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post #3 of 13 (permalink) Old 06-18-2017, 03:43 AM Thread Starter
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Great points, I appreciate the input.

That's a fascinating design. I can see the appeal in some cases. I think for what we want to see in the tank, however, its not for us. But the points you mention are valid across both baffle types, and has gotten me thinking.

You are absolutely correct, that i was thinking about flow incorrectly. Or, more accurately, starting in the wrong place to emulate it. Volume will have to be considered for sizing pumps, but you are 100% correct in that I need to start with velocity, and then i will be able to figure volume based on the size. Good call.

So in this case...lets just say, for simplicity sake, that we are figuring moving the entire water column of the tank dimensions, ignoring the substrate, decorations, baffle area of the race track, etc. So a 1" water column, front to back, top to bottom is about 3 gallons. So if I wanted to move 1-2" per sec, then that would be 3-6 gal per sec, or 10,800 - 21,600 gph. That's a lot. lol. Thankfully the area won't actually be that big. Additionally, constricting the flow with larger rocks in certain parts will create a smaller area, so therefore a faster current, so I think that's the ticket. So with that in mind, i was thinking 2 pumps, with a max of 4000 gph each at max setting, but would use a lower setting 90% of the time. Does this math work out?

I really am leaning towards the racetrack type, after putting MS Paint to work again this afternoon. The plumbing and equipment to do an external recirc system have proven to be extensive. And a lot of drilling. below is what i mean.



Again in green is a double layer of egg crate on both sides to smooth the flow out. Then from both the top and side views you can see there would be 9 holes drilled, and 3 pumps in use. Knowing that there would be a differential in output of three vertically stacked openings, I already want to rethink that design so the output of one pump is split laterally rather than vertically, but you get the idea. Either way, I'm not sure I'm in favor of this approach. It would have the safety aspect, since its a closed system. But its a big gamble to drill all those holes, and then if it doesn't work how i hoped, I'm stuck with 18 holes.

Does anybody have any other design ideas to get a nice, linear flow going? This much volume is certainly a challenge.


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post #4 of 13 (permalink) Old 06-19-2017, 02:56 PM
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This is exactly what I plan to do. The divider to encourage a laminar flow. I haven't started anything yet.

Am trying to figure out what filter system, powerheads to use etc.
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post #5 of 13 (permalink) Old 06-19-2017, 03:16 PM
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Aquaclear 70 (old 802's) power head's would be my choice.
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post #6 of 13 (permalink) Old 06-19-2017, 03:31 PM
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Quote:
Originally Posted by scolba View Post
Right now the river is at its seasonal low flow, of around 250 cfs at a specific measurement point. How do i go about converting that to a lower end of flow rate through the tank, and then adapt that to an appropriately sided pump? https://waterdata.usgs.gov/nwis/uv?p...gif_mult_sites

250 cf/s = 1870 GPH flow.

Convert gallons US per minute to cubic feet per second | flow conversion

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post #7 of 13 (permalink) Old 06-19-2017, 04:17 PM Thread Starter
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I think you actually have that backwards....1870 is gallons per second. Using that calc you linked, it shows that 250cf/s is 112200 GPM. But instead of dividing that value by 60 (which would figure per second) you should multiply it by 60 to get hours. So that makes GPH 6,732,000. Quite a few more. lol.

But all that is inconsequential without a known area, so that's why going after the flow calculations based on velocity is the correct approach like @theatermusic87 was saying. I appreciate the link to the resource, though!!


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post #8 of 13 (permalink) Old 06-19-2017, 04:24 PM
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Quote:
Originally Posted by scolba View Post
I think you actually have that backwards....1870 is gallons per second. Using that calc you linked, it shows that 250cf/s is 112200 GPM. But instead of dividing that value by 60 (which would figure per second) you should multiply it by 60 to get hours. So that makes GPH 6,732,000. Quite a few more. lol.

But all that is inconsequential without a known area, so that's why going after the flow calculations based on velocity is the correct approach like @theatermusic87 was saying. I appreciate the link to the resource, though!!
Hahaha, oops!

Yeah, I'm pretty sure that 6,732,000 GPH flow would be a little overkill hahahaha.

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post #9 of 13 (permalink) Old 06-19-2017, 05:12 PM Thread Starter
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haha, a little overkill.

So just for funzies, lets say we did setup 6.7M GPH across this tank, using the basic measurements, not figuring for any area constriction with rocks, etc. 1870 gallon per sec would be 593.65 inches per second, which would make 33.7 MPH. Haha. That means that literally only the top 10 fastest fish in the world could keep up with that rate. haha. Top 10: What are the fastest fish in the world? | Science Focus

Ok, that was fun.


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post #10 of 13 (permalink) Old 06-23-2017, 03:30 AM
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wow this is so technical for me to understand!! but it was a bit informative though since I'm having flow problems in my tank.


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post #11 of 13 (permalink) Old 06-23-2017, 05:36 AM
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Google "River manifold Loach tank" for some simplicity in set up's for riverine fishes one might be considering.(Some DIY involved)
For planted tank's, one can adjust spray bar's to provide surface rippling or directional flow along with powerhead's if needed/wanted.
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post #12 of 13 (permalink) Old 06-23-2017, 04:37 PM Thread Starter
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Hey RM, thanks for the input! I'm familiar with the River Manifold setup....but unfortunately, I don't think it would work in a tank this large. If my flow calcs are right....which is a HUGE "if", I need to target 8000 gph for 1.75" per sec flow rate in the fastest part of the tank. I haven't been able to find a powerhead that seems to go with the river manifold setup that would be good for 2000 gph (so I could use 4 of them). I could be ignorant of their existence, though, so If you know of some, I would sure appreciate a make/model!

Thanks!


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post #13 of 13 (permalink) Old 06-23-2017, 05:32 PM
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Have you looked at using a smaller sized baffle for most of the back then open up at the end to distribute flow? Forcing the water in a smaller space will add your velocity at the same GPH. Opening the baffle to full height at the end will allow you to distribute the flow to different levels effectively, and having a baffle half the height would allow you to get hardscape/plants underneath it.
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