DSB with undergravel filter

[MarkD40]

I fully understand the value of a DSB in the removal of Nitrate. What I don't understand is why an undergravel filter would not increase the amount of nitrate removal and make it more efficient.

If the sand bed is deep enough, as the water gets pulled through the upper layers of sand aerobic bacteria would use up the oxygen in the water while breaking down ammonia and nitrite.

As the water passed through the deeper layers of sand it would become anoxic allowing anaerobic bacteria to break down nitrate. The water would then pass up the stand tube and be re-oxygenated as it is ejected forcefully from the powerhead.

Without an unergravel filter, this action would need to take place solely by diffusion which would be very slow and inefficient.

What am I missing here? Somebody help me out!

[BurntOutReefer]

the flow-rate thru the sand would be to high (fast)....it would work with a slow rate thou....IMO

[YoungReefer06]

I fully agree with you, I think a very thick sand bed made over an undergravel filter powered by slow flow powerheads would be more efficient then a stagnent sand bed.

IMO you will reach anaerobic activities in sand with an active flow though it if the sand is deep enough.

I have been researching this because i have a new larger refugium i have that i want to set up and i can make the sand up to 14 inches deep.

[3D-Reef]

MarkD40,
The only problem with an under gravel filter is that detritus will build up underneath it.Then flow will slow down,causing a reduction in filtration.IMO Then you would have to tear it all apart to clean it.
I have read about a system that uses a reverse flow up through the sand.I think its at a fish store.I left my book at work otherwise I'd give more info.
FWIW I run a RDSB and the nitrates stay at 1-2.5 ppm.Infact I'll probably have to start dosing kno3.(for the plants)
Clay

[MarkD40]

Thanks forthe feedback Clay. If the sand bed was only say 2-3" deep I agree that detritis would accumulate underneath the undergravel plates. If the the bed was deep enough with finer sand on top wouldn't the detritis only go down only so far and stop at some point and never reach the area under the plates? Sand stirrers would keep the upper layers broken up until all of the detritis was be consumed no?

[billsreef]

With a slow flow, and a very deep sand bed, it could work in theory. I'd imagine the sand bed would have to bo on the order of a foot deep or possible deeper in order to achieve the necessary anoxic conditions. Considering the same effect could be achieved with a 4-6 inch DSB with no forced flow, why bother with the extra equipment?

[YoungReefer06]

I was palnning on making it 14 inches deep.
Why the extra equipment? I already have it in my fish room. The REMOTE REVERSE-FLOW UGF underneath a DSB will be abl to process more nitrate since ith has a flow though it but still has the nessasary anoxic conditions.
Am I not right?

[billsreef]

Even if you have the equipment laying around (you ought to see my basement ), setting it up might be more hassle than is needed in reality. For instance I've run DSB's and fed heavily, and had no detectable nitrates in any DSB tank set up I've run. In fact for my Sea Grass tanks I find I need to add nitrates IMO for the typical hobbyist tank set, I think your trying to solve a problem that doesn't exist.

However, I do think it could be a quite interesting experiment for systems with very heavy fish loads or with large heavy eating fish like groupers, sharks, etc.

[3D-Reef]

I agree with Bill.
The system I spoke of earlier is used by the Tropicorium in Romulus Michigan.He uses a RDSB for his coral farm.The sand is suspended middle of the tank and has pressure from the bottom up.Which,IMO,would keep the "dead spots"to a minimum.A more even flow through the bed, so too speak.
If you set up a system,pm me I'd like to come see it.
Clay