Building a Moving Sand Filter

[Ulu]

I want to build a DIY moving bed or fluidized bed sand filter, and I'm looking for advice from folks who have built one or use a commercial one.

What would you do different?

Do these things eventually sandblast the inside of the container? I would like to see the sand moving and I was just going to build a plexiglass box.

I use a small moving bed sand filter on my 30 gallon sump as an add-on to the biological filter media.

It runs off a small power head and it seems to work great but allows very little flow, unfortunately. This thing claims to filter an enormous 300g tank but the flow is pitiful. It looks like about 30 gallons per hour on a 60 GPH powerhead throttled way down. 1/4" pipe would handle it.

Of course this is why I want to build a large one. Something suitable for a 1" to 1.5" feed pipe.

It has been running for about a month Out of Doors where it can also grow a little bit of algae but it does not seem to. The tank it serves however is well coated with algae. The plastic appears to be UV resistant but I don't know if this has an effect on the growth of biologicals. The whole business has only been set up a minimal time and it was seeded with the materials of the previous aquariums.

By the way, you can see all of this in my patio tank thread under General Aquaria.

 

[islandguy11]

I want to build a DIY moving bed or fluidized bed sand filter, and I'm looking for advice from folks who have built one or use a commercial one.

What would you do different?

Do these things eventually sandblast the inside of the container? I would like to see the sand moving and I was just going to build a plexiglass box.

I use a small moving bed sand filter on my 30 gallon sump as an add-on to the biological filter media.

It runs off a small power head and it seems to work great but allows very little flow, unfortunately. This thing claims to filter an enormous 300g tank but the flow is pitiful. It looks like about 30 gallons per hour on a 60 GPH powerhead throttled way down. 1/4" pipe would handle it.

Of course this is why I want to build a large one. Something suitable for a 1" to 1.5" feed pipe.

It has been running for about a month Out of Doors where it can also grow a little bit of algae but it does not seem to. The tank it serves however is well coated with algae. The plastic appears to be UV resistant but I don't know if this has an effect on the growth of biologicals. The whole business has only been set up a minimal time and it was seeded with the materials of the previous aquariums.

By the way, you can see all of this in my patio tank thread under General Aquaria.

I think that's the nature of many kinds of reactors -- not sure what type that one was originally designed for. If as a nitrate reactor then too much flow would make it harder to create an anaerobic environment for such bacteria to thrive.

I tried (for just a short time) a bit different style Aqua-Macro Nitrate Reductor MBE-22 (using biomedia and bioballs) and the return came out a drip tip that was super slower even than yours, ~5 gph. Personally I questioned how could it have any substantial effect on the nitrate level at that flow rate but I'm not sure as I didn't use it long enough.

 

[fishdance]

I have used fluid sand filters commercially and DIY.

They are especially good for accomodating sudden increases in bioload (heavy feeding, introducing large numbers of fish or big fish etc). They are commonly mis-used as supplementary filtration but having extra or large sized filters don't add value as they are limited by the bio load as food source.

They do take a long time to establish maturity and that small volume filter can easily handle a 300g tank. I would not bother increasing the size or water flow.

In most commercial situations they use wide surface area - shallow filter tanks of sand as oxygenation can be a problem. Effective nitrification consumes lots of oxygen. The biggest downfall is compaction especially if the power fails. And having sand near water pumps so back flow needs to be eliminated. For DIY, I use an inverted witches hat (the roadside safety cones) as the initial flow is stronger by design. Sand uplift drops naturally as the diameter increases since water velocity drops. With the filter directly in the tank itself if possible. And put water pump on backed up power. There are other methods to ensure an initial churn kickstart such as a narrow parallel input pipe creating laminar flow or having a central standpipe high enough that gravity head is sufficient or having a wide base plate (like yours) or a wide shallow sand filter tank.

You will not gain any advantage by having a wider pipe or higher water flow or more sand churn. You will have to replace sand media more frequently as it becomes too smooth faster. But if you just want to play around then why not..

 

[fishdance]

Island guy - if you are trying to create a denitrator reactor, the simplest (most foolproof) and economical method is to buy a 300m or 600mm roll of black 4mm micro irrigation pipe and put through a very very low flow rate (dripping). It will become anarobic somewhere and the long dwell time will strip nitrate. Don't use clear tube or algae will grow producing oxygen. Any cheap black narrow pipe will do but the micro irrigation rube is very cost effective and conveniently has lots of different connectors to join or branch or drip etc.

At slow drip rate this can go back to your tank directly if you don't have a sump or re-gassing chamber.

 

[Ulu]

. . . You will have to replace sand media more frequently as it becomes too smooth faster. . . ..

How often would the sand need changing? Would you change 100% at once?

 

[Ulu]

Island guy - if you are trying to create a denitrator reactor, the simplest (most foolproof) and economical method is to buy a 300m or 600mm roll of black 4mm micro irrigation pipe and put through a very very low flow rate (dripping). It will become anarobic somewhere and the long dwell time will strip nitrate. Don't use clear tube or algae will grow producing oxygen. Any cheap black narrow pipe will do but the micro irrigation rube is very cost effective and conveniently has lots of different connectors to join or branch or drip etc.

At slow drip rate this can go back to your tank directly if you don't have a sump or re-gassing chamber.

Is it possible this will work with brackish water?

 

[duanes]

I built the one below.

In the plans, from an old FAMA (fresh water and marine aquarium) magazine, it had a screw on top, and was pressurized.
I found this to be PITA because during power outages, water would back siphon, and plug up the feed pipe (even with a check valve), so I removed the top and used large enough a pipe to simply overflow to my sump. (1.5" PVC overflow pipe) This was if power went out, I could simply pull the plugged pipe, and tap out the sand, using flexible pipe to pump water into the filter/reactor, but rigid PVC in the reactor itself.
The fluidized tube is about 4 ft tall, 6-8" in diameter, made from clear PVC, and normal PVC parts.
I have also made smaller ones, 3" in diameter and a foot tall.

I used aragonite sand as media, to help buffer pH, beside as biomedia, this is also where the open top came in handy.
As aragonite dissolved, I'd just pour in a few spoonfuls of new sand.
It can be use in fresh, brackish, and salt water situations.

Just after adding new aragonite, the water would temporarily get a bit milky colored, as you can see above.
I made it tall, to allow tiny media grains, room to move, without overflowing to any or sump at high pump age rates.

 

[Ulu]

I'm less enthusiastic about the sand filter, after my first real long run of the little Lifeguard Aquatics device.



When I attempted to clean the unit after about 6 weeks of aging, it wasn't running well. I attributed this to dirty sand, but it was sand in the pump. Despite my efforts, the pump is now worn and weak.

Frankly I give this one a zero for design. OK, maybe 0.01~0.05, just because the clear plastic is really thick and sturdy.

It is fairly simple, but you cannot open the top. You have a 1" dia hole to fill it with sand, and that hole is the bore of the throttle valve. The valve is a rotating sleeve valve, which went out of fashion long ago as difficult to clean and prone to galling. One grain of sand and the fit is ruined. It had grit which seized the sleeve, and with much difficulty I wrestled this apart with a 16" channel-lock pliers.

I rinsed the sand in a bucket, as it is impossible to back flush. I added some aragonite sand to replace about 1lb of lost sand, and reinstalled it, but the action is weak, and I don't have a spare pump that will work.

Anyhow, I have learned a lot experimenting with this one, and I think the major thing I've learned that the lid must come off. Also the throttling must not use a conventional valve.

If I continue to use this one I'll put plastic media in it and add air, but my initial idea was I needed an aragonite reactor. This wasn't it.

While it's bad form to look a gift horse in the mouth, and it was free, so far it wasn't worth my efforts. I'd been better off to improve my conventional filter sump.

 

[fishdance]

Are you disappointed with the rainbow lifeguard or fluid sand filters generally?

Fluid Sand Filters are poorly understood. It may take 6 months for the bacterial to colonies successfully and they don't do any mechanical filtration so they never need to be cleaned (ever). Slow flow that stirs is all that is needed. They are dull boring reliable and extremely effective. Just safe guard against back flow and top up worn media as needed.

 

[Ulu]

Are you disappointed with the rainbow lifeguard or fluid sand filters generally?

I like the idea, and I will build a different sand filter, but I don't like the Lifeguard filter design at all.

The tiny fill hole for the sand is also a valve!

Some idiot thought it would be a good idea to take apart the valve to add sand thru a tiny hole?

It's still running, but it's now building up algae inside, above the sand level. Since the top is glued on it's impossible to remove algae.

Fluid Sand Filters are poorly understood. It may take 6 months for the bacterial to colonies successfully and they don't do any mechanical filtration so they never need to be cleaned (ever). Slow flow that stirs is all that is needed. They are dull boring reliable and extremely effective. Just safe guard against back flow and top up worn media as needed.

It's only been cycling for two months.
Maybe I will run it from a standpipe or add a bleeder to prevent backflow.