Has Anyone Done This?

[Frank]

I was thinking about an undergravel filter, with the outlet connected to overflow plumbing, then down to an ordinary sump.

[Cory]

Sounds like if the gravel ever clogged, your tank would flood. I'm not sure many would have tried this.

[gardenman]

It's kind of backwards. An undergravel filter is a biofilter more than mechanical and biofiltration is typically the last step in the filtering process. If you're using a sump and an undergravel filter you'd be wisest to use the undergravel filter in a reverse flow configuration where the water coming back to the tank from the sump, where it's undergone mechanical filtration and is physically clean, is then forced up through the bed of the gravel where the bacteria living in the gravel can consume the dissolved ammonia, nitrites, etc.. This would also keep the gravel clean as water rising from the bottom through the gravel would sweep debris up and into circulation where the overflow could grab it and and send it to the sump where it would be removed mechanically. If you do it the way you propose there would be no place for physical debris to go other than down into the gravel and that would eventually clog the gravel. 

[Frank]

43 minutes ago, gardenman said:

It's kind of backwards. An undergravel filter is a biofilter more than mechanical and biofiltration is typically the last step in the filtering process. If you're using a sump and an undergravel filter you'd be wisest to use the undergravel filter in a reverse flow configuration where the water coming back to the tank from the sump, where it's undergone mechanical filtration and is physically clean, is then forced up through the bed of the gravel where the bacteria living in the gravel can consume the dissolved ammonia, nitrites, etc.. This would also keep the gravel clean as water rising from the bottom through the gravel would sweep debris up and into circulation where the overflow could grab it and and send it to the sump where it would be removed mechanically. If you do it the way you propose there would be no place for physical debris to go other than down into the gravel and that would eventually clog the gravel. 

It wouldn't be the first time I did things backwards...

My thought was to use water circulation to help gravity to settle out debris. I hate seeing the same piece of poop swirling around for two days. 

Thanks for the help!

[Andy's Fish Den]

Or, if your sump is large enough, you could put the undergravel filter in a section of the sump, like what Cory did in the sump of the 800 gallon tank. 

[Frank]

13 hours ago, Cory said:

Sounds like if the gravel ever clogged, your tank would flood. I'm not sure many would have tried this.

That potential issue would be prevented by using simple plumbing.

 

[gardenman]

1 minute ago, Frank said:

That potential issue would be prevented by using simple plumbing.

 

The open top tee fitting would prevent the tank from overflowing, but a largely clogged gravel bed would render the gravel bed ineffective as a biofilter. Using a gravel bed as a mechanical filter could work, but then it's not as effective as a biofilter. Floating debris is best removed by a powerful HOB or canister filter. Even the effectiveness of the gravel bed as a mechanical filter would slow as the gravel bed clogged. 

[Squeegee79]

I think the first question here is "What are you trying to solve by doing this?"

The sump filter, if set u with bio balls/bio rings/etc. will be a way better biological filter than the UG ever could.

[Tanked]

32 minutes ago, Frank said:

My thought was to use water circulation to help gravity to settle out debris. I hate seeing the same piece of poop swirling around for two days. 

If your goal is to settle out debris, than you might try powerheads on the UGF if you aren't using them already.