Stationary Sand Bed Filters
Public aquariums typically use very large stationary sand filters to do the mechanical and biological filtration. Because the public aquariums use a small sand volume to fish weight ratio (.e. a lot of fish for a small amount of sand), they must backwash these filters daily, typically on a computerized automatic cycle. The biological filtration is done very efficiently by a thin hard biofilm that is created on the sand particles.
Because the sand particles are so small the surface area of these filters is simply staggering. A well-set-up sand filter will have two to four times the capacity of an equal volume of fluidized K1 bed. But there are no designs of these stationary sand beds that will work for the aquarium.
In Tank Stationary Sand Beds
Cory from Aquarium Co-op found a huge wholesale fish facility in the Netherlands that had the backwall of each aquarium (about 1,000 aquariums, all identical!) a sand bed where a relatively small flow of water flowed down through some filter floss, up through an air tube, then down through a bed of very coarse (2 millimeters?) grey sand that looked like blasting media to me, then back up through another tube into the aquarium. The sand filters were low flow and never cleaned.
This system unfortunately requires that the water level in the aquarium only be at roughly 75% of capacity. Not something that will work for a decorative aquarium. But it has given me an idea for an innovative sand bed filter that would work on a decorative aquarium. I’m working on it.
Pool Sand Filters
Stationary sand filters are used for pools. These are cheap, $250 to $350 for the unit without the pump.
The problem with these pool sand filters comes when the water flow hits the fabric that keeps the sand in the filter. Pool water has chlorine and thus doesn’t clog this fabric with biofilm. Aquarium water will clog this fabric pretty rapidly with bacterial biofilm and the flow will stop.
Modified Pool Sand K1 filter
Rachel O’Leary came up with the idea of taking a pool sand filter casing, removing the sand and the fabric filter, and filling it with K1 media. Attach an external aquarium pump. This is a very good idea. It gives one a very low-cost, high-capacity filter, especially if one can find a used unit at a pool supply store. Note that K1 is an excellent stationary filter media as shown by testing. K1 does not have to be fluidized to work well. Filling the unit with plastic pot scrubbers would also work very well.
The inlet and outlets of the pool sand filter will have to be modified to make quarter-inch holes act as the media retaining strainer. If the fabric that comes with a pool filter is used bacteria will clog it up with biofilm in short order.
Small Aquarium Fluidized Bed Sand Filters
There are some companies which sell a third type of sand filter, a small fluidized sand bed. These were considered the optimum aquarium filter until K1 fluidized bed media came along. K1 is very superior to sand as a fluidized media not because it is a better biofilter (it isn’t) but because K1 fluidized bed doesn’t require an engineering degree to install it and keep it running.
At the current time the only sand filter I can find used for aquariums in the USA is the Lifeguard Fluidized bed sand filter.
The following comment from a user of this system, Robert E Holt, is pertinent:
“The Lifeguard, once installed seems to work well. Plumbing it was a bit of a pain, and I had an issue with it leaking initially, but have not had a problem keeping the sand suspended. The biggest problem is, it is designed with too many options. There are 4 different locations for hose connectors. and a valve on top to adjust the flow. Each of these openings offer opportunities for the unit to leak. I found the valve to be useless and a major source of leaks.
I almost gave up on it, but was able to seal the valve, in full open position, as well as the other connections, and install ball valves on the inlet, in order to adjust the flow. In order to not restrict the flow on the canister filter, I also installed a bypass, with another ball valve. The canister filter is filled with 30 ppi foam, providing additional bio filtration, and acting as a prefilter for the sand filter.
The system has now been running for 2 months with no apparent loss of sand. Ammonia and Nitrite are always 0 and the water is crystal clear. The plumbing is a bit of an eyesore, and I am not sure I would go to the trouble again, but now that it is in place, there is no recurring maintenance and it seems to be doing its job.”
I.e. only consider a fluidized bed sand filter if you like “fiddling” with a very complex system. Note also that this hobbyist is using a foam-filled canister as a “prefilter” to the sand filter. So is the crystal clear water because of the sand filter or is it because of the canister filled with foam? Good question!
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But note that this is a very good filter at a very reasonable price. It will filter a lot of fish load very efficiently. It is two to three times more efficient than fluidized bed K1 sumps and easily ten times more efficient than a canister. But note the small size of the unit.
This filter is also easily converted to a K1 fluidized bed simply by plumbing in an air stone, with some loss in efficiency as the K1 is not as good as sand as a media. And it should be noted there are several “do-it-yourself” designs of this sand filter on YouTube. They are all way too complex for my tastes. In my experience, the more complex any device is, the more unreliable it becomes. I like good old “KISS” designs, “keep it simple stupid”.
I do NOT recommend fluidized sand bed filters!
They are NOT simple to operate.
Also note that the designs I see on YouTube of these sand filter devices all use PVC plumbing that has several glaring errors. First of they do not abrade the joints nor do they use primer. Then they do what are called “butt” joints, the pipe is cut so small the fittings butt up against each other. And they wrap their Teflon Tape in the wrong direction.
These errors will produce leaks. Indeed, the first go around for one of these YouTube video makers had leaks all over the place. Which this person “fixed” by doping on huge quantities of adhesive. aahhhahahmmm … This person is an ……. OK … OK … I won’t use that descriptive term.
Startpage Aquariumscience
Source: Aquariumscience.org – David Bogert
