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Undergravel Filter Flow Requirements


tolstoy21
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I'm looking to build a DIY undergravel filter for a 30 gallon aquarium. 

Do these require a specific amount of flow to operate efficiently, or can one be operated with a gentle amount of flow provided by an air stone?

Would a small powerhead be a more preferable option instead of an air stone? 

I'm looking to set this up in a betta tank.

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Under gravel filters are great because they function on very minimal flow, so an air stone would be fine. The downside is that due to the low flow nature of under gravel filters, they can take longer to fully establish. If your bioload is going to be low or gradual, then an air pump is fine. A powerhead will be quieter, but your betta probably won't appreciate the higher directional flow output as much as it will the gentle bubbles. I know people who have been running the same UGF for over a decade just on air, so that's a testament to how effective they are.

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I have an undergravel filter set up in a 10 gal yellow fin white cloud tank that is working well. It depends what you want the tank to do. 

 

If you have high flow, either a powerhead or tall uplift tube, then stuff will get sucked in and gunk things up. I went low flow. 

 

I cut an uplift tube just above the substrate and have an airstone in there. I just want low flow to get water through for the bacteria. I'm trying to get a lower oxygen level at the bottom of the substrate for nitrate reduction. I have a thin layer of fluorite red on the filter plate, and then a thick layer of Safe-T-sorb over that. I had to wash both well. 

I have 0 ammonia, 0 nitrites, but still getting nitrate so I  think my plant level is too low. I have 10 adults and about 8 to 10 fry growing up in the tank now. Its been set up for about 2 months.

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Thanks for the advice everyone.

I'm going to put one together soon and will test out different options

For those of you who DIY these, are there any recommendations for spacing out the slits (openings) in the PVC under the substrate? Do you get less draw from the part of the PVC furthest away from the uplift? Can this be accommodate for in the design in any way, for instance like with more openings, or wider opening further away from the uplift? 

I guess I can run a bunch of different scenarios and find out. I'll just have to find something to put in the water during testing to visually understand the draw strength from different parts of the tubing under different uplift rates, or to just verify that it doesn't matter at all. But I'm going to guess, how substrate compacts and gunks up over time will also affect this in many ways under normal operation.

Anyway, always fun to tinker. Gives an aging man something to think about other than real work!

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I'm posting a cover photo of a booklet produced by the University of Delaware many, many years ago and photos of the pages from inside showing the construction of a DIY undergravel filter to help you out. To give you some idea of how old this booklet is, the price for a 20 gallon tank then was listed as $17.94.  I believe it was published back in 1975, but there's no copyright. 

 

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I posted a similar question on Tuesday.  My primary question being: how much air volume is needed to be efficient.  While the question remains unanswered, The consensus was that a low to moderate airflow through an air stone is adequate. 

 I prefer powerheads on the UGF.  There is no doubt that they are drawing water through the gravel, provide water movement and aeration, and aren't reliant on lift tube height, so  you can hide them.  The only real downside that I see in your 30 gallon is that depending on your installation, a powerhead that is too large might blow very small fish all over the aquarium.

I do not think that distance is a contributor to draw strength. Negative pressure should be the same across the distance. Water will always take the path of least resistance , so larger/more holes or thinner substrate would be bigger factors.

 

Edited by Tanked
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Just to follow up on my previous post. I think a reverse flow UG filter with the water coming from a canister filter and then the mechanically filtered water gently flowing up through the gravel bed makes the most sense for a DIY project. You need no uplift tube at all and can simply put the spray bar for the canister filter under the UG filter plate with just the return hose going down. A filter made and run in that manner would not disturb your betta at all. There would be less likelihood of the gravel clogging over time. Wastes should stay in suspension and be easily filtered out by the canister while the gravel bed did the heavy lifting of biofiltration. The spray bar would distribute water relatively evenly across the width of the UG bed. It would be a very nice, gentle, easy filtration system for a betta.  You can get canister filters for tanks as small as 10 gallons for well under $100 also. Using a canister filter in this manner might cause more wear on the filter as it's pumping the return water out against the water pressure in the tank, but I doubt that it would be a huge problem.

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18 minutes ago, Tanked said:

There is no doubt that they are drawing water through the gravel, provide water movement and aeration, and aren't reliant on lift tube height, so  you can hide them.  The only real downside that I see in your 30 gallon is that depending on your installation, a powerhead that is too large might blow very small fish all over the aquarium.

Yeah I'm going to try to go minimal on this, like probably just an air stone with a USB pump.

I'm going to use some furniture-grade black schedule 40 PVC for the construction of this.

This tank is going to be in a 'public' area of my house and my wife is a stickler for not seeing lots of equipment or filters inside the tank, hanging off of it, and/or tons of dangling wires and tubes. I don't disagree.

For this tank I'm hoping all one will see is the jet-black uplift against black substrate and a black background.

This tank is 24" deep. So I guess you're suggesting uplift tube height is not something that needs to be factored into the design? The shorter I can make the uplift, the better hidden it will be within driftwood, rocks, etc.

The folk sat Jehmco recommend extending the uplifts on some of their large box filters for better draw. So I was imagining the same would be true here. But, like I said, I have no real experience with this (yet!)

Edited by tolstoy21
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8 minutes ago, gardenman said:

Just to follow up on my previous post. I think a reverse flow UG filter with the water coming from a canister filter and then the mechanically filtered water gently flowing up through the gravel bed makes the most sense for a DIY project. You need no uplift tube at all and can simply put the spray bar for the canister filter under the UG filter plate with just the return hose going down. A filter made and run in that manner would not disturb your betta at all. There would be less likelihood of the gravel clogging over time. Wastes should stay in suspension and be easily filtered out by the canister while the gravel bed did the heavy lifting of biofiltration. The spray bar would distribute water relatively evenly across the width of the UG bed. It would be a very nice, gentle, easy filtration system for a betta.  You can get canister filters for tanks as small as 10 gallons for well under $100 also. Using a canister filter in this manner might cause more wear on the filter as it's pumping the return water out against the water pressure in the tank, but I doubt that it would be a huge problem.

Thanks for the thoughts. However, I'm planning on a very minimal design and wasn't going to do reverse flow. No canister filters or sponge filters, etc.

I saw a PVC UGF on amazon and thought, jeeze, I could easily make that with a bunch of scraps I already have.

Edited by tolstoy21
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10 minutes ago, tolstoy21 said:

Thanks for the thoughts. However, I'm planning on a very minimal design and wasn't going to do reverse flow. No canister filters or sponge filters, etc.

I saw a PVC UGF on amazon and thought, jeeze, I could easily make that with a bunch of scraps I already have.

Using scraps to build fish tank stuff is TIGHT!  
note: cause in my posts I talk about me using scraps to build most of my stuff!!
Low flow, I use the $10, now $14 air pumps from walmart, cause I used to be able  to shop there.

Edited by aehageman
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3 minutes ago, tolstoy21 said:

This tank is 24" high. So I guess you're suggesting uplift tube height is not something that needs to be factored into the design? The shorter I can make the uplift, the better hidden it will be within driftwood, rocks, etc.

I believe that lift tube height is not a factor when using a powerhead.  I would think that taller is better with an air stone.  In any event, black tubing against a black background will almost disappear.  Add a strategic plant or rock and the wife will be happy.

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1 minute ago, aehageman said:

Using scraps to build fish tank stuff is TIGHT!  
note: cause in my posts I talk about me using scraps to build most of my stuff!!

Yeah the only thing I'd need to buy is black tube for the uplift since I don't have that on hand. Other PVC, elbows, airline and some random air pumps i all have sitting around already waiting to become useful.

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3 minutes ago, Tanked said:

I believe that lift tube height is not a factor when using a powerhead.  I would think that taller is better with an air stone.  In any event, black tubing against a black background will almost disappear.  Add a strategic plant or rock and the wife will be happy.

New technology and research has proven that the longer your inlet tube/s the more flow you will gain. Powerheads receive less increase relative to their already high flow rates, where as air powered increases exponetially as the lenght of the tube is increased.  (Hey! No spell check in this editor! WTF [worse than failure])

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2 minutes ago, Tanked said:

I believe that lift tube height is not a factor when using a powerhead.  I would think that taller is better with an air stone.  In any event, black tubing against a black background will almost disappear.  Add a strategic plant or rock and the wife will be happy.

I was planning on starting with a 12" uplift tube, which is half the tank depth and I'm guessing should be sufficient to at least start with.

I'll be sure to post back some pics and info / observations as I start this (hopefully soon).

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6 minutes ago, tolstoy21 said:

Yeah the only thing I'd need to buy is black tube for the uplift since I don't have that on hand. Other PVC, elbows, airline and some random air pumps i all have sitting around already waiting to become useful.

I am looking into painting..  Also I store my PVC in tanks with lots of light.  so the get covered quickly with green growth.  The wife commented in the beginning about the pipes, but not so much now.   The more green growing on them the better.  there is a post here about painting, but that is time and expenses and well how long till the paint comes off and leaches into  the water. 
I read that taking a bit of sand paper to the PVC increases algae growth on the pipes, so going to start trying that before paint.


Here is an idea to help hide that sightly equipment.  You just need a camera, a color printer and some double sided tape, (or know how to fold tape back on itself.
In this  post they show how to do it with your monitor,  hope you get the point.
These Illusions are created by taking a digital photo of your surroundings then place it as the desktop background of your monitor
 or screen. That way, they appear to have a fully transparent display.
https://www.hongkiat.com/blog/creative-transparent-screen-trick-photos/

 

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11 minutes ago, tolstoy21 said:

Turn spell check on in your web browser!

Most web platforms assume that either your operating system or browser has that capability already, so it's rarely built in these days. But now I'm getting off topic!

Thanks, but I do this for a living.  I was raised in ARKANSAS, so I rely on spell checker and my wife to edit / rewrite most of my important emails, but not my hobby posts. So, spell checker is ON, just NOT for this editor!!    Stop distracting me, stay on target!  STay on target !  LOL! Use the force Luke!

I have some designs for under gravel filters using 1/2 and 3/4 pvc.  Testing pin holes and slits   Seems slits, long thin polygonish cuts in the pipe work better than pin holes as the pin holes become clogged much quicker.  (as you will learn my tanks are very dirty compared to the prestine tanks @Cory likes to show in his images and videos.  I don't have that kinda time, nor do I care about seeing through the majority of my glass.  
Any hoo!
I am about to try some old vacuum cleaner tubing under some lave rock.  I bought a thing for my dremil that might cut the slits easily.  Soon as I figure out the best way to post from my phone to this forum CMS I will post images.  
Low flow UGF  is the way to go, if you want a sustainable ecosystem in your tank. IMHO!

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If your looking to custom build an undergravel filter check out Amazon, it has some modular undergravel filter plates  to install. I've got some on order to set up in a large tank like either my 90 or 75 gal. You could glue your own fitting to the plate that would fit any uplift tube you want. Far easier to adapt what is out there rather that reinventing the wheel.

 

Other have done a pvc network under the gravel with slits cut into it. If you are looking for a more even flow pile up more gravel near the uplift tube and slope it shallower the further you go away from it. I use only one uplift tube on my filter plate cause I want very low flow.

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  • 2 weeks later...

Just thought I'd share the UFG I put together this weekend.

Nothing fancy, and I wont go into much detail as this is the standard PVC DIY UGF. Instructions for this can be all over the internet and YouTube.

But I will add the following . . . 

I used 3/4" furniture grade black schedule 40 PVC for the uplift tube since it was more attractive and had no printing, etc. This kind of PVC can be found in a good reef store, or ordered pretty inexpensively through Home Depot.

The air is driven currently by a Coop USB pump with a very slender air stone I salvaged from a broken Lee's box filter. My feeling was that a standard air stone might not have enough clearance around it to updraft water correctly.

To cut the slats in the PVC under the gravel, I used my Dewalt mitre saw. I can set the depth of the cut on this so every cut is the same (give or take). I used a fine-toothed blade (the same blade I used to do finish work like cutting moulding). The larger toothed blades can shatter the PVC instead of cutting it, which can be quite dangerous . Yes I found this out the hard way a few years back!  A good mitre saw makes many tedious jobs much easier and faster. You'll never regret the money spent on one. 

Next step is driftwood and some plants.

Ok enough talk, now for some pics . . .

 

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Edited by tolstoy21
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