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"REVERSE" flow under-gravel filter


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Some people think that under-gravel filters are bad because of a build up of mulm under the filter plate. There is disagreement among the hobbyists as to whether or not this mulm build up is good or bad.

I use my under-gravel filter "REVERSED". That is, I place power heads at the top of the lift tube with the output of the power head blowing down into the lift tube there by reversing the flow of water up (not down) through the gravel AND at the same time washing away any mulm that may have collected under the plates I have found that by using this "REVERSED" method there is very little need for gravel vacuuming. The water passing up through the gravel bathes the debris at that has fallen on the gravel breaking it down to be swallowed up by the filter. The result is crystal clear ammonia free water.

However, I would welcome and comments about this topic..... pro or con.

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On 6/29/2021 at 8:41 PM, preswash said:

Some people think that under-gravel filters are bad because of a build up of mulm under the filter plate. There is disagreement among the hobbyists as to whether or not this mulm build up is good or bad.

I use my under-gravel filter "REVERSED". That is, I place power heads at the top of the lift tube with the output of the power head blowing down into the lift tube there by reversing the flow of water up (not down) through the gravel AND at the same time washing away any mulm that may have collected under the plates I have found that by using this "REVERSED" method there is very little need for gravel vacuuming. The water passing up through the gravel bathes the debris at that has fallen on the gravel breaking it down to be swallowed up by the filter. The result is crystal clear ammonia free water.

However, I would welcome and comments about this topic..... pro or con.

Can you share a video? 

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I like the idea of using the output from a canister filter to feed the reverse flow UG filter. Use the gravel bed as your biofilter and the canister as the mechanical/chemical filter. It would take a bit of siliconing to lock the output hose into the UG input, but it would be doable. It would create positive pressure under the gravel bed with a constant flow of water through the gravel bed. The backpressure on the canister filter pump might shorten the canister filter lifespan a bit, but spray bars also create backpressure on the filter so I'm not sure how much of an impact it would have. That's the approach I would take if I were doing one today. Canister filters have gotten pretty cheap and an approach like that might be ideal.

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On 6/30/2021 at 9:07 AM, gardenman said:

I like the idea of using the output from a canister filter to feed the reverse flow UG filter. Use the gravel bed as your biofilter and the canister as the mechanical/chemical filter. It would take a bit of siliconing to lock the output hose into the UG input, but it would be doable. It would create positive pressure under the gravel bed with a constant flow of water through the gravel bed. The backpressure on the canister filter pump might shorten the canister filter lifespan a bit, but spray bars also create backpressure on the filter so I'm not sure how much of an impact it would have. That's the approach I would take if I were doing one today. Canister filters have gotten pretty cheap and an approach like that might be ideal.

No silicone was needed to attach the cannister to the undergravel....there were adapters that were made to do exactly that.  Also there is no back pressure to the cannister that I could detect...it ran that way for years with no issues and I still have that cannister today.  It worked very well.   

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Yes I use my hot Magnum 250 to drive the reverse undergravel filter on my 36 bow front with one plate from a Lee's 75 undergravel.

I'd be interested in anything anyone has to say about gravel vac over the reverse flow undergravel filter plate. I have found that there's very little debris in my vacuum tube when I'm vacuuming over those areas the only area that I find the normal gravel vac debris is in a dead spot where there's no undergravel plate

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