DIY RFUG for Spec V (or Spec) - Opinions Welcome - The Planted Tank Forum
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post #1 of 6 (permalink) Old 07-25-2013, 01:27 PM Thread Starter
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DIY RFUG for Spec V (or Spec) - Opinions Welcome

I apologize beforehand for the glacial pace I do all my projects at - kids, the house, work, life, etc. have a way of getting in the way of our hobbies.

Anyway, I recently purchased a Fluval Spec V (haven't set it up yet) and read that one of the issues it has is its inability to suck up and filter mulm collecting on the substrate. Inspired by The Big Buddha and others building a Reverse Flow Underground Filter in this thread...

I decided to start building my own.

Playing around in the local hardware store (and in my basement), I discovered two things:
1. 1/2" ID, 3/4" OD vinyl tubing slides somewhat tight over the Spec's outlet nozzle once the flow director is removed.
2. That same vinyl tubing slides nice and snug into the socket of 1/2" CPVC fittings.

So I picked up the following materials:
4 - 1/2" CPVC Elbows
3 - 1/2" CPVC Tees
1 - 1/2" CPVC Street Elbow
1/2" CPVC pipe
1/2" ID, 3/4" OD Vinyl tubing (short length)

So, the interior layout of the Spec V is nominally 6"W x 17"L. I wanted to set up a manifold that would have 3 long runs parallel to the back of the tank, all connected in a loop. To keep the "sphere of influence" of each run equal, measuring along the centerline of each pipe, I wanted the loop to be 4"W x 15"L - this makes that so-called "sphere of influence" extend approximately 1" from the pipe centerline in all directions.

I also decided that I wanted to have a "hard-piped" riser from the filter manifold to the outlet nozzle, connected by a short section of vinyl tubing serving as a Fernco coupling. The nozzle's centerline is approximately 9.25" from bottom of tank.

So, I cut the following lengths of pipe:

2 lengths of 14-1/8" to serve as the "longer" front runs
1 length of 12-5/8" to serve as the rear run that the riser will rise from
1 length of 8" to serve as the riser
4 lengths of 1-1/8" to serve as short runs between the long runs - this gives just enough room between fittings to drill an outlet hole

Here's all the parts cut and lined up

Here's a mock setup of the RFUG (note that the street elbow is connected directly to the riser tee, saving me from cutting a piece of CPVC. The tubing will be cut to size prior to installation.

I still have to figure out how many outlet holes to make and what diameter [any suggestions?]. I plan to array them in a "zigzag" pattern within the two parralel "box loops" of the system. I will also drill outlets on the exterior of the entire loop to help clean and oxygenate between the system and the tank walls/.

Last edited by wintermute; 07-25-2013 at 03:34 PM. Reason: added photos
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post #2 of 6 (permalink) Old 07-25-2013, 09:31 PM
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You can use a simple formula to decide on hole size and number of holes. You want the total area of the holes to be a bit less than the area of that hose feeding it. So, if "D" is the inner diameter of the hose, "d" the hole diameter, and "n" the number of holes:
d = or less than D divided by the square root of n. Or, n = or less than the square of "D/d".

If you use 1/16" diameter holes, and the hose inner diameter is 1/2", then n should be 64 or less.

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post #3 of 6 (permalink) Old 07-26-2013, 10:53 AM Thread Starter
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Good advice from the RFUG Guru - KISS! Thanks Hoppy, I was having flashbacks to one of my college design projects - designing a discharge diffuser for a wastewater treatment plant. Finite elements analysis galore - we could vary the length and diameter of the main pipe, the number, diameter, and spacing of the diffuser holes - a nightmare.
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post #4 of 6 (permalink) Old 07-27-2013, 04:44 AM
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I look forward to seeing the results.
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post #5 of 6 (permalink) Old 07-27-2013, 11:10 PM
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If you put the outlet holes on the bottom of the tubes it works best. That keeps substrate out of the tubes, makes it very unlikely that roots will enter the holes, and gives the maximum thickness of substrate for the water to pass through, avoiding little "volcanos" at each hole.

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post #6 of 6 (permalink) Old 07-28-2013, 03:36 AM Thread Starter
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How about 45-ing them out from the bottom? I want to have outfalls on the interior and exterior of the loops

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