By Bob Goemans
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Bob Goemans corresponds with Rico Horton

Rico Horton writes...

Hi Bob

Thanks first and for-most for the great help you give to us in the aquarium world.

I was recently given a nice rectangle glass 55 gallon tank and was wondering if a deep plenum sand-bed will be too heavy for this glass tank. Also I saw your 180 gallon tanks with an external plenum sump. Do you think that would be the best way to go with the glass tank? If so what size sump would work with plenum for a 55 gallon glass tank? Also was wondering if regular aquarium undergravel filter plates that can be purchase at any aquarium store will work as a plenum grid verses the egg crate build it yourself type?

Thanks for your help,

Rico Horton

Mountlake Terrace, Washington

Bob replies...

Hi Rico,

Good questions, and actually one's I've not seen for a long time. As for the weight of a deep sandbed in a glass aquarium, unless it's going to be moved sometime in the future with the sand in it, that additional weight now is not a structure problem. Actually, it's the weight/pressure of the water that is the biggest stress factor.

Nevertheless, having the plenum in the main tank does make it difficult to maintain it correctly, unless sparsely decorated with live rock. Keep in mind the bed surface is somewhat like the surface area of a filter pad. As water flows through that filter pad, matter clogs it and it will eventually need cleaning if it's to remain effective. The same is true with the sandbed surface, as the plenum bed must be vacuumed, as should any sandbed surface (usually once a month), to remove 'settling' matter that will eventually clog its geo/bio pathways. Especially with plenum beds, as there is the possibility that sand grain binding may occur in some areas, as there are fast forming bacteria colonies. Binding also occurs if the dissolution of calcium carbonate sand is retained in the bed because there is higher than normal (natural seawater) levels of calcium in the bulk water, which is sometimes purposely maintained at significant higher levels to help push stony coral growth. Therefore, it's far easier to maintain it in an interconnected tank, which in your situation could be 10 - 20 gallon tank. The 10 would be fine for a light bioload, with the 20 better suited for something higher in bioload.

As for using an UGF plate, history has shown its holes/slots are too small and/or not sufficient enough to maintain the transference of elements and compounds over a long period of time, e.g., over a year. History that I have shows those that went that way have systems no different than a deep bed directly on the aquarium bottom in the long run! And even though some said their nitrate levels were far reduced, they had unwanted algae problems because the bed now produced too much ammonium, one of the main causes of extensive algae growths! If you take the time to read my plenum articles on my website, that ammonia issue will become very clear. And if building your own plenum grid is too much effort, go to my website and click on 'Custom Made Plenums' on the Links page. They will make whatever you need for a very fair price.

Hope this helps,



Undergravel Filters; Plenum; Deep Sandbed Method

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