# Sand as a filter media



## Tom S (Dec 28, 2009)

Has anyone ever tried using sand as a filter media for polishing water? Sand should have o problems with removing any small bits of debris we find in aquarium water to give very clear and clean water after filtering.

My research shows lots of pressurized sand filter used for pond filtration, but the problems I see with this is that the buildup of debris is forced into the sand, making it hard to clean effectively and causing the filters to become clogged over a short period of time.

I am thinking of a system could be set up in a sump, as tower for the water to enter the sump though. Top layer would be a coarse sponge, which would catch the larger debris and could be easily removed and cleaned. It would also break up the flow to prevent the water cutting channels through the sand, and could provide and area biological filtration. Under the sponge would be a layer of sand, I'm thinking 2"-4" thick. If this layer it two think the water will take a long time to pass through, and if the layer is to thin it could be washed away. A layer of lava rock under the sand would keep it from being washed out the bottom, which is where the filtered and polished water would exit.

The sand used should not be overly fine, as this would reduce the flow through the filter and cause problems with clogging. A coarser sand such as Pool Filter Sand should work well, is easily available, and can be replaced every once and a while without a large cost.

Any thoughts/ideas/input? Purely concept at this point, but I think it could be made to work with a bit of forethought.


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## tirzo13 (May 26, 2004)

Sand is used in a FBF Fluidized Bed Filter, but it works because the sand is flowing.

In a canister or HOB filter, it would simply impede the flow of water.
Lava rock works much better in this situation.


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## BillD (May 17, 2005)

Sand will work as it does for swimming pools, and PFS will filter down to a particle size of 20 microns. On pools the sand is cleaned by back washing. Swimming pool sand filters have been used to filter aquaria, usually in stores with a large tank or numerous tanks in a system.


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## RRasco (Aug 31, 2006)

I posed the same question a while back and FBFs were brought up. I was thinking the same as you, using sand in a sump as the filter media. I was thinking about 2 inches of sand at the bottom of two compartments. A baffle dividing the compartments about 1" off the bottom of the sump. As you suggested, not sure how much sand would be moved around as opposed to the water flowing through it. I still want to try it one day.


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## fmueller (Jan 11, 2004)

Personally I don't think it would work, because like tirzo13 said, the flow rate through the sand would be too low. That said, I'd be happy to be proven wrong by anybody willing to give it a try :thumb:


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## tirzo13 (May 26, 2004)

If you could fluidize the sand as in a FBF it would work, otherwise you are creating a dead environment which is more suited to anaerobic bacteria (bad kind).

aerobic bacteria (good kind) need flow and oxygen. FBF are able to achieve that by fluidizing the sand.
a regular filter achieves it by having bigger spaces as in bio balls, lava rocks etc.

if you restrict the flow in such a compact space, anaerobic bacteria (bad kind) take over.

It may be able to be done, but i think there is a certain practical reason why manufacturers use bioballs for biological media, and filter floss etc for polishing or mechanical filtering.


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## fmueller (Jan 11, 2004)

Tirzo13 is making some good points. However, the catch is that the OP wants to use the sand to provide very fine mechanical filtration. An FBF only does biological filtration, not mechanical. Any particles will pass freely through the fluidized sand.

I'd also agree largely with the general categorization of bacteria. For the fish keeper really anaerobic means bad, while aerobic means good. Some people try to confuse this matter by pointing out that there are anaerobic bacteria that can complete the nitrogen cycle by converting nitrate to nitrogen, which would gas out of the tank into the air. Air consists to 80% of nitrogen anyhow, so there would be no ill effects. That's true in principle, but the water of any healthy fish tank is highly oxygenated. Wherever the water flows, there will be oxygen, and anaerobic bacteria will die. Only where there are stagnant areas with no water flow anaerobic bacteria will thrive. Since they don't come in contact with flowing water, they can serve no useful purpose, but they can produce toxic compounds that can be harmful to fish once these areas are stirred up.

Sorry for digressing slightly, but I do think these issues are relevant and should be considered when contemplating the design of a sand filter.


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## RRasco (Aug 31, 2006)

Not today and not tomorrow, but one day I'm going to do it. Even if just for a proof of concept. They use them for ponds and pools, no reason we can't do so with an aquarium. Just because something is possible doesn't make it practical. Only one way to know for sure...


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## fmueller (Jan 11, 2004)

RRasco said:


> Just because something is possible doesn't make it practical.


That is probably the key. I have no doubt there is some way to get tank water through sand, and surely that sand would filter the water. I just reckon it's going to be a lot more complicated than using a sheet of foam or some filter floss. Certainly sand is cheap, but it isn't like filter floss or foam are the things in this hobby that are breaking the bank.


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## tirzo13 (May 26, 2004)

Prefilter on the intake of the FBF, boom instant mechanical filter.
thats how i run mine.


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## M&amp;S (Feb 16, 2011)

We did build and run a filter using gravel and sand once (not for an aquarium though). We had three levels, the top was 5-10mm gravel, the next was smaller "pea" gravel, and the bottom was sand.

There's no doubting it cleans the water and provides mechanical and biological filtration.

The ideal scenario would be to have it higher than the tank, pump water up to it, then let gravity take it back to the tank. An overflow could be incorporated (as a seperate pipe) should the filter or outlet get blocked. If I was building a tank I;d probably do this, then I could extend teh cabinet to the ceiling.

I am designing a gravel based trickle filter to sit above my tank, but don't know if I really need it to be honest. The canister and plants do an A1 job. Maybe for you guys who don't have plants though - it will give a polish to the water?


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## Rhinox (Sep 10, 2009)

Hey if you guys are interested, I've got some equipment lying around that would be perfect for a proof of concept experiment. I'm changing my sump over to a HMF soon, and after I do I'll have a couple buckets with a bunch of holes in the bottom and nothing to do with them. I also have a couple filter pads I could put in the bottom of the bucket, pour some sand in on top, and start running water through the sand to see just what happens.

Of course, this will have to be a day when I'm bored and the weather is nice, and my ulterior motive will be to see if it is a easier way to rinse sand but this thread has me intrigued enough to try.


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## Tom S (Dec 28, 2009)

Wow. Thanks for all the responses. I have been busy the last couple days and unable to check the forum.

I most definitely agree that this would not work in a canister or HOB. I think that building a tower-like structure in a sump and letting gravity do the work would be the best way to go about this. I was also worried about anaerobic bacterial, but I think that if you used sand that was on the coarser end of the spectrum and kept the layer of sand to a minimum depth you could keep the flow rate up and not have a problem with anaerobic bacteria.

I would look at building a FBF system, but I am always worried about what happens when the power goes out.


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## mlancaster (Jul 24, 2009)

Although not directly related to setting up a sand filter in a home aquarium; when I visited the back areas of the SF Academy of Science they used huge upright tanks with varying coarsenesses of sand to filter all their aquariums.

For the saltwater aquariums they actually pump water a few miles up from the beach then run it through the sand filter and the other various filters (i.e. carbon etc.) before going pumping it into the tanks.

It was quite interesting to see the process.

As *RRasco* noted, sand is obviously used in certain situations, but is it practical to set up a DIY sand filter for the home aquarium. I guess practicality is not an issue if it is something that interests you.

This is an interesting thread. I am glad it reminded me of the tour of the SF Academy of Science; I recommend going there for anyone living or visiting SF.

Thanks,
Matt


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