Refugium/Sump

[Instar]

If you use a large particulate substrate like 1/4 inch crushed aragonite, use the eggcrate and make it a plenum. In that case you will need a powerhead in place on a lift tube for 8 months to seed the plenum. If you use sand, skip the eggcrate like matt said.

[GaryP]

Larry,

I'm missing something here. Maybe you can set me on the correct path.

It would seem to me that there is greater permeability in coarse substrate than fine. Therefore there is greater vertical migration of water through the low oxygen gradient at the bottom of the DSB. It makes sense that you would need a deeper coarse than fine sand bed to establish the gradient for denitirification to take place. Isn't the purpose of a plenum to increase that circulation. So I guess the question is why would you use a plenum with coarse instead of fine substrate. That seems to be the opposite of where my logic leads me, unless the plenum itself is the anaerobic zone and the coarse sand is only serving as an oxygen stripper to get to a low enough Redox potential for denitrifying bugs.

Please let me know where I am going astray in my logic here.

Thnx,
Gary

[Henry]

Gary here is a link that discusses plenums

http://advancedaquarist.com/issues/sept2002/feature.htm

[Tim Marvin]

Plenums are a filter of the past. People are finding they crash on them and wipe out the entire tank. If you use too fine a sand they clog up and that is what causes the instant death to your tank. I wouldn't recommend a plenum unless your are an expert reef keeper and have a place to move all the livestock when it crashes because you can't fix a plenum with everything in the tank. If you build one outside of the main tank you'd better have a good eye and move fast when it starts crashing. From what I understand Scott Morell from GARF is no longer useing a plenum due to a crash, and I am not sure if GARF is useing them either.

[matt]

Cool article; I have a feeling that one reason plenums get kind of a bad rap is because they seem to be pretty specific and complex to set up correctly.

[Tim Marvin]

That is what I understand. They need to be totally dark or they will produce O2 from algae down deep. They also need the correct sand sizes. Too complicated for me to try so I can't give first hand advice. I feel that you should either have an experts eye or do lots of water testing every couple days to monitor these filters. We are haveing such great results with refugiums and "Matt's monster skimmers", why grasp at other filters, especially since they do the same thing and are easily monitored. I say go with what works.

[GaryP]

Tim,

At some point I read a bunch of info that really hyped plenums. I also met an LFS owner that installed him in all of his tanks. I was thinking about putting one in my next tank. Then I started see some of the negative stuff and just went to a DSB. I had run either bare bottom or shallow coarse sand beds before that (not knowing any better). Still, I thought I had some understanding of how they worked. I can see the problem with fine sand and a plenum now that I think about it. It would be difficult to find one with a fine enough mesh to keep my sugar sand from infiltrating into the plenum.

BTW, the LFS in Pineville, NC that Pete gave the link to above is one of the finest shops I have ever done business with. Its primary business directed at reefkeepers. Its fairly small and new but the owner (Tommy) is one of the most knowledgeable I have ever met. When you asked him a question, you didn't get an answer, you got a lesson. The are the driving force behind the local frag club and host the meetings as well as arranging joint meeting with other frag clubs in surrounding areas. They had a great frag tank that had frags for anywhere from $5-20. They were also raising their own frags. I was doing about $100/mo. in trades with them when I lived there. I only wish Tommy would franchise a shop here.

Gary

[Tim Marvin]

Do you stay in contact with him? I'd be interested in how those plenums are doing. Sounds like a great guy, we need more lesson givers than just sales people. A lot less trauma to livestock if people had a short lesson before a purchase.

[GaryP]

Tim,

No, unfortunately I haven't stayed in touch. I moved from there last April. I just thought it would be good to plug a well deserved LFS for a change, even if its 1400 miles away. I dropped Pete a PM and asked him to say hello for us. There was a definite "family atmosphere" at Hi-Tides. Its nice to go to a shop where you felt more like family than a "sucker."

The staff at the only other SW LFS in the Charlotte area were paid on commission. Need I say more?

Gary