RFUG - A Blast from the Past - DIY - The Planted Tank Forum
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post #1 of 140 (permalink) Old 12-14-2008, 03:01 AM Thread Starter
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RFUG - A Blast from the Past - DIY

One problem I never seem to get away from is finding a way to get good CO2 concentration all over the tank. I can and do set up a Koralia powerhead to give me a circular water circulation all around the tank, but as the plants grow, that circulation gets slower and slower. So, I am tired of fighting that battle.

It has occurred to me that, in nature, most plants get their CO2 from the substrate, so ideally we should inject our CO2 under our substrate, but my idea of using silicone tubing leaking CO2 into the substrate didn't work out. Tom Barr suggested using a RFUG, reverse flow undergravel filter, instead. Lots of time spent researching the internet to see if anyone has succeeded in using a RFUG to distribute CO2 returned nothing. But, I did find that Tom was extremely enthusiastic about them back in 1999. So, I decided to give it a try this week.

The goal for a RFUG is to distribute water uniformly under all of the substrate, to use the whole bottom of the tank as a gravel filter. And, if you first filter the water with a canister filter, the substrate can act as a "polishing" filter only, but if that canister filter water is also passed through an external CO2 reactor first, the evenly distributed water will evenly distribute CO2, right at "ground level" for all of the plants, solving the problem of how to reliably get CO2 to all of the plants, all of the time.

Tom had a couple of other suggestions, dating back to 1999, make your own filter grid from PVC piping, and put the water exit holes in that piping under the tubes, so substrate material can't flow down into the tubes. That is what I am doing.

My design criteria were:
Minimize the canister filter flow reduction caused by the RFUG.
Achieve uniform flow from all water exit holes without having to adjust hole sizes and spacing.
Keep the cost as low as possible.

Tom prefers to use CPVC piping because it comes in smaller diameters, reducing the room the filter tubes occupy under the substrate. I chose to use standard PVC because of the ease of buying all kinds of fittings for it.

I designed this as an under gravel manifold, which means minimal flow velocity in the tubes for even distribution of the flow to all holes. And, I made use of standard fittings for every part of the RFUG. The finished product, before gluing any connections or painting the stand pipe black, looks like:


and the water exit holes are shown here - 7/64 inch holes on approximately a square grid pattern.


All of the piping sizes and the hole sizes and number of holes are designed to reduce the effect on the flow from the canister filter and give uniform flow from all holes. To check whether this works right I stuck a garden hose on it and with the holes pointing up, I compared the height of the fountain of water from all of the holes. It was almost exactly the same for all holes.

There is no need to glue any of the pipe fitting joints, since there is very little pressure on them, and PVC fits tightly into the fittings anyway. But, I will glue those connections that could cause water to flow all over the floor if they slip loose. And, to minimize the visual disturbance from the standpipe I will paint it black with Krylon Fusion. The brass valve is sold as a drain valve at Home Depot - it will help bleed the air from the unit when first set up and every time the canister filter is cleaned.

I hope to set this up by the middle of this week.

Hoppy
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post #2 of 140 (permalink) Old 12-14-2008, 03:06 AM
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Very cool! I look forward to seeing this in use and its affect (effect?) on the plant growth

-Chris

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post #3 of 140 (permalink) Old 12-14-2008, 03:08 AM
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Sounds very interesting !!

If it works many of us will try it ! I'm one of them
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post #4 of 140 (permalink) Old 12-14-2008, 03:12 AM
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I'll be interested to see how this works. This is a spin off my 6' spray bar in the back of my tank. A few ????

1. Will the CO2 get to the leaves? Isn't it the leaves that need the CO2?
2. Will the flow be so little as to keep the mulm and such from clouding up the tank or causing a new tank cycle issue?
3. What if anything will this do to the nutrifying bacteria that needs O2 to grow and thrive.
4. Will this get in the way of planting and roots?
5. Would it have been better to have this lay on the VERY bottom and elbowed ports come up every 5 square inches to avoid questions 1-4.

Don't really know if these are any issues but I do wonder.

Just keeping on keeping on....


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post #5 of 140 (permalink) Old 12-14-2008, 03:34 AM
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that's a really good idea!

have you ever had to unclog a line from a leach field from a septic tank? for some reason (and i think it might may apply here) roots and debris seem to really like to get into those holes and clog them up... is that something that's likely to happen? maybe a screen for the holes? i might just be tired...
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post #6 of 140 (permalink) Old 12-14-2008, 04:03 AM Thread Starter
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Of course I don't know how well this will work, and I know there are potential problems. Texgal, this will sit on the bottom glass, with about 3 inches of substrate on it, which means non of this will be within 2 inches of the surface of the substrate. The CO2 will be in the water arriving from the canister filter and external reactor, so it wil have no place to go but up under the leaves, whether still in solution or released as gas bubbles. The flow shouldn't be high enough to affect the mulm at all, I think. But, at worst it might cause more of it to migrate to the canister filter inlet and be filtered out.

The purpose of nitrifying bacteria is to neutralize ammonia, but I plan to use a zeolite sand as a substrate, and that will adsorb some of the ammonia, and the plants should take care of the rest of it. It may interfere with some plants and roots, and roots may grow into the holes, at least partially blocking them, but I hope the flow through the holes is strong enough to help stop that.

The reason for releasing the CO2 enriched water down in the substrate is to use the substrate as a diffuser to spread out the flow more uniformly.

I enjoy trying new things, even if they are old things.

Hoppy
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post #7 of 140 (permalink) Old 12-14-2008, 06:49 AM
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interesting experiment.. Root feeders might not do so well with current in the substrate.


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post #8 of 140 (permalink) Old 12-14-2008, 01:36 PM
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Will the CO2 be on 24/7 or on a timer/controller? Some things perhaps worth noting along the way are weather there is an increase in substrate acidity. I am unsure why you decided to use a zeolite substrate. Doesnt Zeolite release back into solution ammonia once it reaches capacity? In a glass bottom tank, it may be worthwhile to have a peek on the underside of the tank if it is on a stand that allows this to note root growth. My experience in the days of yore was that UG filters grew great roots but not terribly good plants in total. But most of all a big thank you for going to the extra work of documenting and sharing this trial.
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post #9 of 140 (permalink) Old 12-14-2008, 02:26 PM
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interesting idea i look foward to seeing your results.
dont you worry that after the can takes most of the oxygen out of the water and with the lower flowyou might encourage anaerobic bacteria ?
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post #10 of 140 (permalink) Old 12-14-2008, 02:50 PM
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Very nicely done and also very interesting. Kudos to you for trying this!!!!

The only problems that I see is:

1. CO2 lock in the tubes.
2. Also some holes may get blocked causing uneven CO2 distribution.

I look forward to hearing about your progrsess on this!!!

BTW what size tank will this be going in and how are you going to determining the effieciency and/or CO2 levels in the tank?

Thanks for sharing!

Last edited by EdTheEdge; 12-14-2008 at 02:50 PM. Reason: I'm a ditz!!!!
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post #11 of 140 (permalink) Old 12-14-2008, 04:03 PM Thread Starter
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Marrow, the CO2 will continue to be on a timer, but, of course the water flow from the canister filter will be continuous. Zeolite absorbs and holds cations, including NH4+, but I can see no mechanism for it releasing it, except to plant roots. I'm sure that it will eventually, and maybe quickly, get saturated so no more adsorption takes place. But, it is a relatively cheap substrate, the cheapest easily available that has a very good CEC. My tank is about 45 gallon size, with a solid plastic support under the bottom glass, so I can't see there. It is about 30 inches by 20 inches high, by 15 inches front to back - curved front glass, so a maximum of about 17 inches front to back. Tom Barr reported back in 1999 that plants did indeed grow very good root systems with RFUG, and those plants did very well, but plants not growing good roots didn't do that well. But, he didn't distribute CO2 with the RFUG, so how that will affect plants is unknown, as far as I know. The very few cases I found where people tried this in the past never included results - a bad omen because people always report good results.

Fraser, I have no idea at all about how this will affect Oxygen in the substrate. I asked Tom about it causing a lower pH in the substrate, and he responded that substrates are such good buffers that it shouldn't cause a problem.

Ed, initially I will try to supply this only with water with dissolved CO2, not with CO2 bubbles or mist. I think CO2 mist would not be a problem, other than the microbubbles perhaps coalescing into big bubbles in the substrate and burping out. Big bubbles in the water would possibly collect at the top where the pipe goes over the top of the tank, but those should be swept along by the water flow, and might burp out of the substrate - if nothing else that would be interesting to see. I will continue to use a drop checker to monitor the amount in the water, knowing how inaccurate that reading will be.

When you try something new or unusual you can always get surprises.

Hoppy
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post #12 of 140 (permalink) Old 12-14-2008, 04:58 PM
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When you try something new or unusual you can always get surprises.
Sometimes pleasant surprises!
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post #13 of 140 (permalink) Old 12-14-2008, 05:12 PM
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Originally Posted by mistergreen View Post
interesting experiment.. Root feeders might not do so well with current in the substrate.
No, they do extremely well, eg Crypts and Swords became monsters/
I used tese for 10 years and is why I got into plants, they produced extremely excellent Sword plant growth to the likes I'd never seen.

I started using them back in the 1980's after seeing a LFS using "Excelon" in typical down flow operation(Not Reverse) and I wanted the sand not to clog the typical plates folks used, so I decided to run it in reverse(less vacuuming as well) since the holes would blow out and always be unsticking the holes, not clogging them, sort of like a low flow Fliudized bed filter(FBF).

The bacteria cycle like mad also(huge surface area) and you produce zones of low redox and high redox with this set up, shaped somewhat like an "egg crate", with more positive Redox(and higher O2) around the outflow and regions of lower Redox around the lower regions away from the out flow from each hole. This gives far far far more experimental flexibility and measures than you can ever hope to get from Heat cables or certainly a GREAT DEAL more than ADA power sand. I can change and vary the flow rate from nothing all the way up to high movement FBF if I want, eg.....moving sand......

Redox is the best in situ measure of flow rates and O2 for plant roots, you can make several spots or push one probe up and down through a range of flows and measure and quantify. By making your own redox probes, you can leae them in the tank over time and measure the redox by simply swapping the Redox meter BNC connector for eahc location. DIY redox probes are often used in wetland sediment research. Tropica also did this back in the 1990s and I discussed it with Claus, who was about the only person I'd met that had a clue.

The same arguements used back then are still the same old myths used today

Some things never change and nothing ever gets answered.
If you believe something, make a test and see if it's true and explore both sides of the coin, not just the side the marketing company sells you

RFUG's are easy and cheap to make. I know there's no use in adding more flow because the optimal flow rates are normal diffusion rates without any added flow(Cables, RFUG, ADA PS etc).

So I no longer use them.
They are good for Vaughn's idea however, adding CO2.
You can make a spray bar along the bottom, just above the sediment blasting from the rear back wall towards the front bottom of the tank for a similar effect without going to a RFUG. You will still need some surface movement with this, so you need additional flow also to move the surface and add O2 etc. You can drill a few holes in the CPVC at the top to accomplish that.



Regards,
Tom Barr




Regards,
Tom Barr
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post #14 of 140 (permalink) Old 12-14-2008, 05:19 PM
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Will the CO2 be on 24/7 or on a timer/controller? Some things perhaps worth noting along the way are weather there is an increase in substrate acidity. I am unsure why you decided to use a zeolite substrate. Doesnt Zeolite release back into solution ammonia once it reaches capacity? In a glass bottom tank, it may be worthwhile to have a peek on the underside of the tank if it is on a stand that allows this to note root growth. My experience in the days of yore was that UG filters grew great roots but not terribly good plants in total. But most of all a big thank you for going to the extra work of documenting and sharing this trial.
Zeolite fills up and can do this, but often, by then, it's well colonized by bacteria, that's it main function for filtration in pools etc, higher surface to volume ratio, and it looks the NH4 at the start, it makes an ideal filter media though and it's cheap.

Once a large colony of bacteria are going and cycling, the system is very stable. Unlike many methods for sediment, you can move plants all over without issues since the system is pretty aerobic and very responsive to organic nutrients and NH4.

It's like having a huge sand filter.

Regards,
Tom Barr




Regards,
Tom Barr
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post #15 of 140 (permalink) Old 12-14-2008, 07:41 PM
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from what I've read, a medium redox is preferred by roots. High redox will let micronutrients stay in its oxidized form and plants can't use it. Circulation in the substrate would cause a high redox or more likely, higher than usual.


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