putting Plenum into the tank

[h2o]

1. Do I must completely move all water out of tank to put plenum down? or if it's okay to have water when putting it in. what about water in the pvc?
2. I will be using standard size window screen on top of eggcrate. At the edge of eggcrate, do i fold the screen down to the eggcrate, or spread it out to the tank floor? the instruction on this site got me a bit confused.
3. Burnspy mentioned putting only one screen, but this site says 2 layers or screen. What is your opinion.
I will be putting aragonite on top of the eggcrate, then ls. please correct me if i am wrong. thanks.

 

[h2o]

anybody?? please.

 

[myreef]

IME, if you are actually putting down a full blown plenum, then you probably need to take out any rocks you have in there, but not the water. Just keep in mind the water displacemnt when you add the sand. Most people these days just use a deep sand bed (DSB) instead of the plenum. You will find proponents of both. I have used both and like the DSB just because it is easier to install. HTH good luck.

 

[h2o]

Andy, so you mean it's ok to have water in tank while putting plenum in. But then there's will be water in the pvc pipe and underneath the eggcrate, is that alright?

 

[oceanblue]

H2O,
yes it's ok, think about it, the only way to keep water out anyway is to seal it off. The idea here is to have very slow water exchange so that the anaerobic bacteria don't get any oxygen but still have contact to the source of nitrates..that is their food afterall and the whole idea behind it. good luck with it, I'm interested in hearing if people really think they've got the benefit from a plenum or dsb versus the risk.

 

[sonny]

It is fine to have water in the PVC pipe. In fact, you should drill holes in the PVC to let water in. When you put it in, you can first lay down a piece of screen, then put the plenum grid in, and fold the screen over the top. Add another piece on the top to make sure you cover the whole thing. When you get your sand for the system, grain size is very important. You want four inches of 1-4 mm size grains on top of the grid. Any smaller and it will fall through the screen, and any larger will allow too much diffusion, which will make the system less efficient. Make sure your grid has plenty of support, as the sand and live rock are quite heavy. Also, for the best use of the Live sand, try to stack your rock in a way to keep it elevated above the sand bed, allowing water movement under the rock. This can be done by making small "bridges" between smaller rocks at the bottom. Live sand has tremendous filtering capacity, so the amount of live rock you need will be less!
Sonny

 

[h2o]

thanks Sonny. a bit confused, If I have screen top and bottom of the eggcrate, what about the pvc pipe. should I not glue to pvc to the eggcrate grid. or do you mean the screen to be on the floor and wrap around the pvc and eggcrate? thanks.
In preparing for this coming project I am ordering 40pounds of Natural Ocean from this site. I also called my local **** Depot to locate Southdown sand, but the manager told me Southdown Inc. has been acquired by another company and they no longer deal with SouthDown, Only have quickcrete sand. anyone use this brand before? how is it.
thanks a million.

 

[beth]

I think you're confused about the layering.
Flat on the floor of the aquarium goes the 1/4-1/2" PVC, this allows for water flow space at the bottom of the bed [or plenum]. Atop the PVC goes the eggcrate to fit snug around the perimeter of your tank, on top of the eggcrate goes a fiberglass screen [not metal!] which is what keeps your substrate from falling thru the larger-hole eggcrate into the plenum area. Now you place your first layer of courser sand to be followed by yet another screen, then live sand on top.
Now, if you are not going to have sand sifting creatures, you can eliminate the first layer of sand and the 2nd screen.
You will have better maneuverability if you remove your water and start this process with an empty aquarium.

 

[myreef]

As stated above, you can have water in the tank when you do it. Just be prepared for the sand to make the water cloudy when you are done. Do not use the quickrete sand. Either find the SD sand or use arragonite.
I have one tank withe a DSB and one with a plenum. I really think the DSb is better than the plenum. I can't give any concrete evidence why, but the overall appearance of that tank looks better. I have had success with a plenum system before, so whichever way you go, you should be fine. HTH

 

[andymi]

If you cannot find the southdown sand I would recommend maybe using the CaribSea brand of aragonite. I personally use a plenum system and layered it with CaribSea special grade. It is supposed to solve multiple purposes. 1. It is your substrate. 2. (From what I have read) When the aragonite dissolves over time it will help release vital nutrients into the water which helps keep calcium up if I remember correctly. My plenum system has been up and working for approximately 3 months without problems and I have seen places that have used plenums for 15+ years.
I also removed all of my sand and rock into rubbermain containers ( i started with a DSB ) and put my plenum in with water still in the tank. So far so good
HTH
-Andy

 

[sonny]

The PVC should be connected to the grid. I recommend using plastic cable ties to connect them, as you don't have to wait for glue to dry. You can glue it if you want to though. Lay down the screen, then the plenum grid, then make sure the top of the grid is covered completely with screen before adding the sand. There should be one inch of space under the sand. That includes the grid. If you use 3/4 inch PVC pipe, that should give you the right height. You don't want the plenum to be butted up to the edge of the tank either. They work better with complete darkness. DON'T put any sort of lift tube, as this will then be an undergravel filter, not a plenum. The depth of the sand should be four inches. You may put in a screen about two inches deep if you plan to have digging animals in the tank. The lower two inches of the bed should not be disturbed, as this will keep the oxygen level too high. What you are looking for is a anoxic condition, or very low oxygen. I recommend the CaribSea "Special grade reef sand." I also don't like to mix the grades, like having crushed coral on the bottom and sand on the top. My opinion.
Sonny

 

[h2o]

Thank you all for the responses. caribsea sands are rare in SF Bay Area, Lukily I found a store but only carry 15lb for $18.99 internet sells $24 for a 40lb w/o shipping cost. I purchase a sepecial grade for the bottom and a regular Caribsea aragonite, and 2 20lbs of Nature Ocean LS. So with 2 more NO from SWF I hope that's enough (110lb) for 55g, that also cost me a lot of $$. I custom cut 1" pvc with as many holes as I could drill, and will use cable ties. Hope things will work out fine. Thank you very very much.