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FAQs on Reef Filtration: Plenum Alteration, Media Addition

Related Articles:  Reef Filtration, Plenums, Biological FiltrationMarine Substrates

Related FAQs: Plenums 1, Plenums 2, Deep Sand Beds,  & FAQs on Plenum: Rationale/Use, Design, Installation, Operation, Troubleshooting/Repair, & DSBs 2, DSBs 3, Nitrates 1, Nitrates 2, Nitrates 3, Nitrates 4, Nitrates 5, Nitrates 6, Nitrates 7, NitritesAmmonia, Establishing Cycling, BiofiltrationPhosphate, Silicates, Biological Filtration, Fluidized Beds, Bio-Ball, Wet-Dry Media 1 Denitrification/Denitrifiers, Wet-Dry Filters,

Some animals don't take kindly to large/sudden changes in their environments

Plenum Question -- 03/18/08 To the saltwater gurus, <<High praise indeed!>> I just set up a new 55 gallon with a 15 gallon refugium. <<Neat>> I had a plenum in my last tank and everything worked fine. <<Okay>> This time around though I didn't read like I should have and here's the problem. I added the eggcrate, then the mesh barrier, then 3 ½-ish inches of aragonite instead of a dead layer of substrate. <<'¦?>> Will this work or do I need to tear it out and fix it? <<Mmm, I'm unsure of what you mean by 'dead layer'...but I don't see why the Aragonite material wouldn't work, or even be 'preferred'>> Also do plenums need powerheads? <<How do you mean? If for circulation/flow within the tank, yes, just like any other system. If on some type of riser-tube as part of the Plenum itself, no, as this turns the Plenum in to an unwanted 'under-gravel filter'>> I have one set up with a piece of pipe down into the plenum and had one last time but I'm thinking less movement would be nice so if I could take this out it would be great. <<Ah, I see'¦you definitely DON'T want this, as explained>> I know everyone has a different opinion on plenums and I don't really lean either way. <<Pushing water through the Plenum with a powerhead defeats its function (as well as forces in/traps a lot of detritus)'¦for the Plenum to 'work' it relies on/requires the 'natural' diffusion of molecules through the substrata>> The last either helped or did nothing for my tank and since I still had the eggcrate I figured what the heck? Why not? <<Hmm'¦just a simple DSB for me, thanks>> Thanks in advance. Tucker <<Happy to share. EricR>>

Recycling a plenum 1/26/07 Hi <Hello.> sorry if I'm asking a stupid question but here it goes. <My friend, you know better than to think thusly..> I had a 75g marine tank set up with a plenum, 60 lbs of live rock, 4 small fish. I had a wet dry filter (actually I disconnected it at the time) and a small protein skimmer. It served me well for several years. The problem I had was heat. Everything was fine until the last year of operation when the water temps got too high. (I have the tank set in a wall ) I intend on buying a chiller before I  make the tank operational again. My (stupid) question is this. It's been 3 years since the tank ran. I still have the plenum intact (such as it is without water) should I tear down the tank and remove the sand or might I start the  plenum again with new water and fresh live rock? <If I understand you correctly, you have a system that you drained some time ago, but you left everything more or less intact. If the plenum and rock are all still in the tank and waiting for water to cover them again, then you will be disappointed by the amount of life resulting from this quite dead substrate and rock. If you are only desiring biological filtration from this arrangement, then it will suffice. However, most enjoy the elevated levels of live inherent in LS and LR, and are well served to purchase the two that way. Again, you can have a healthy system without adding anything but water of the proper temperature and salinity, but I believe you would enjoy some new substrate, and at least 20 lbs of LR.> I really enjoy your site. I am  very happy with the wealth of info. <As is the all-volunteer crew. By the way, that wasn't a stupid question at all.> I intend on starting a modest reef tank this time Zoo, Ricordea, Acanthastrea, and maybe xenia. <Good choices, all. R. floridae was my first ever photosynthetic invert.> All added slowly over time. I appreciate your time. <Good luck, and read some more of the "wealth"! -GrahamT.>   Thanks   Dave R

Removing undergravel filter Experts of WWM: <Hi Ron, MacL here with you tonight.>   I have recently been doing research about the removal of an undergravel filter from an already established FOWLR aquarium.  (I'm going to leave out all the useless details, of course.)  Anyway, the tank has been set up for a year and a half and all inhabitants seem to be doing well.  The U/G filter has turned into a nitrate factory, as I've learned they always do.  What I would like to do is to remove the uplift tube and cap off the plate.  I have only been able to find one instance (this site) of this being done, so I am extremely worried about doing this.  Anyway, that is my only question. can this be done without a die-off of aerobic bacteria, or cause any type of bloom? <Anytime you disturb your sand (or crushed coral or whatever bed) you will experience some die off.  You don't mention what other type of filtration you have, I'm assuming you have something to handle the filtration once you stop running the undergravel? That being said that you will have some die off the idea is to minimize the amount of die off.  If you can move the sand from around the tubes, then cap them then move it back without disturbing the sand or crushed coral in other areas you have a better chance of minimizing the effects. I think you should be prepared to do a water change in a couple of days regardless depending on the other type of filtration you will be going to. The way an undergravel filter works is pretty simple, it pulls the detritus down through the sand hopefully to end up under the undergravel where the bacteria attacks it. For this reason, once that water stops pulling down you are definitely going to have some changes going on within your tank.> Here are my tank specs: 30 Gal AGA, 96W PC 50/50, Prizm Skimmer with surface skimmer attachment, 40-50lbs live rock (40% Tonga, 60% Fiji), 2-3" crushed coral over U/G filter, powered by Penguin 550 Powerhead. <If you are going to try to go with the Berlin method where the tank is filtered by the live rock then you are going to need the power heads in the tank for oxygenation. If that filtration isn't already established this is going to become much harder to do. Meaning if you don't have bacteria built up in the live rocks and in the crushed coral. This may definitely mean water changes as the tank adjusts to the change.> The inhabitants include: Small yellow tang (to be moved to larger tank at later date), maroon clown, yellowtail damsel, bicolor Pseudochromis, scarlet skunk cleaner, 2 Astrea conehead snails, unknown amount of margarita and abalone snails, as well as blue leg hermit crabs. <Ron I don't want to discourage you, I'm just trying to make you understand the reality of this undertaking.  Let me try to simplify a bit. If your tank is already being filtered in the majority by the live rock then a switch won't be quite so hard. BUT if your tanks primary filtration system is the undergravel then when that stops running you will have some changes take place within your tank.  You probably will have an ammonia rise but that can be handled cautiously with water changes in order to put less stress on your fish.>   Thank you very much, if only for simply reading this.. <I hope I have helped, if you wish to get into this discussion further or have any questions just let me know. MacL> -Ron Narozny, Jr. Abandoning an UGF in a newly set-up 90 gal marine tank and feeding triggers Hi gang,<Hi Ed, MikeD here> I think you guys are doing a wonderful job.<Thanks, we try> My question is I have a 90 gallon fish only that has been up and running for 1 month, it took 3 weeks to cycle,<Be careful. in that short a time even the tiniest glitch can cause it to re-cycle or go into a mini-cycle.> the first question is I put an UGF in before I saw your site, I have 2 300gph power heads running on the up tubes, is this ok or should I get rid of the UGF, I have 6 inch crushed coral covering the UGF, and is it ok to just pull the tubes and cover up the holes without removing the UGF.<This would be my suggestion. I've done it in the past with no problems. On an olde tank you might have sufficient accumulation beneath to warrant siphoning out the mulm, but here I suspect you'll be fine> Second I have 2 trigger and a coral beauty<2 triggers can be a bit much in a 90 as they grow, so consider yourself warned> that are carnivores, I have found that our local Wal-Mart store has in it's sea food section what is called sea food melody, the guy working there said it's just left over and it has squid, clam, crab, and some sort of fish, all raw and unprocessed, I gave ground some up in the food processor and the fish love it.<It makes an excellent food as long as you don't grind it too fine, where it can pollute the tank. Your triggers, for instance have very strong jaws and sharp teeth. I just cut it into small pieces with scissors and feed until they lose interest, then stop> Is it ok, should I add some vitamins?<You can> Last question is I was given some what used to be live rock which I bleached and washed and left out in the hot West Texas sun to dry and let the bleach dissipate, I put it in the tank with my 25 lbs of live rock, I was told it would become live again over time, is it ok to do this?<Yes, it WILL eventually become part of your LR as well> I was told it would be ok, well any way I read your site daily and enjoy it very much.<Thanks for your interest and support> Thanks Ed from West Texas.

Shallow plenum I am in the process of "cleaning up" a 55 gallon 2 year old tank following a hair algae outbreak. I have moved all livestock to another tank except for a Pseudochromis (which I can't catch) to another tank. Also remaining are cleaner shrimp, assorted crabs and snails and a leather soft coral. Ammonia and nitrate: 0; nitrate almost undetectable; SG around 1.021. I have a plenum w/only about 1" of marine gravel on the bottom. Don't really know what it is. Also 25-30# live rock. I would like to add some CaribSea aragonite and/or smaller live sand combination to bring the level up to 2.5-3". What would you suggest? Can I add the live sand on top of the existing plenum, or must I take it all out first?  <You could add it on top, mix it in... a good idea to do about once every six months after a tank has been up a year> Will such an addition throw off my chemical balance to such a degree that I should first remove all of the remaining critters? <No, likely to throw it in the right directions> If not, would a gradual addition or fast addition make any difference?  <Gradual (in two, three divisions) would be better... as would be taking the system apart, putting the new material under the old (between them) with a sheet of fiberglass door screening material> Thanks much. >> You're welcome. Bob Fenner

Some Plenum Questions Bob: I'm thinking about installing a plenum in my 75 G FO system. The tank has only about 45lbs of LR, a DIY wet-dry filter, and an AquaC EV-90 skimmer. Inhabitants are a Naso tang (6"), maroon clown (4"), yellow tang (3"), Paddlefin wrasse (4"), niger trigger (2") and a Huma trigger (3"). Yes, I'm overstocked, and one or more of these inhabitants will be traded in to the LFS when they grow bigger. Nitrates are pretty high despite measures I've taken to reduce them (bottom of wet-dry has submerged Ehfi-Mech and Siporax Beads to host anaerobic bacteria, and a small trash-can within the sump holds Caulerpa and has a light over it). A plenum seems like a reasonably easy and relatively inexpensive way to get additional filtration and nitrate reduction. A few questions if you don't mind..... <Okay, like the explanation thus far> 1) Is it okay to install a plenum into an established tank? <Yes> 2) Is there any particular need for me to remove the wet-dry filter, OR, should I delay the plenum until I've bought enough live rock to take care of biological filtration? <I would delay...> (Not sure when THAT would be; tank is heavily stocked with predatory-type fish, and I'm not sure I can rely on live rock alone). In the meantime, the high nitrates are driving me nuts. <You can, will be able to> 3) If I decide to put the plenum in my sump, how do I avoid the problem of massive gravel going up the skimmer pump?  <Hmm, it won't... this material is too dense to get sucked up> I'm not crazy about having separate sumps; last time I tried this, there were HUGE sucking sounds from one sump to another. The wife is tolerant of my hobby but did not appreciate the "eternal toilet". <Maybe convert the wet-dry sump into a/the plenum> 4) Given my fish load (triggers and such), am I correct in believing that a DSB alone won't work if it's in the main tank, since the fish would likely eat any detritivores and sand-stirring animals?  <Hmm, not a simple yes/no here... both will work, would help> That's why I'm thinking plenum instead of DSB, but maybe you have an opinion on this debate in general or in my particular case. <Mine above> 5) My maroon clown has this annoying habit of sweeping away substrate with his tail, and moving any large pebbles with his mouth. There are huge bare spots on the floor in his territory. Would this kind of behavior cause problems with a plenum or DSB? <She probably thinks you have an annoying habit of sweeping the substrate...> 6) Does Dr. Goemans' plenum scheme in "Live Sand Secrets" work effectively, or is there some other plenum construction plan that I should follow? <Bob G's ideas are very sound here, and in general... his interviews? Bizarre.> Thanks ever so much... <You're welcome, Bob Fenner>

Re: Some Plenum Questions Thanks for your prompt replies -- and for writing "The Conscientious Marine Aquarist. If only they'd initiate a "Fish" category for the Pulitzer Prize . .. Joe <Ahh, you're making my day!> (By the way, where can I find a screen that has a fine enough mesh to keep the oolitic sand from penetrating it? Seems to me I'd have to use a cloth or something similar?) <Yes... I, we just use two, three thicknesses of the inexpensive "fiberglass" screen that we get at "Home Depot" or other such large home improvement outlets... used for screen doors... this works great... Bob Fenner>

Re: Some Plenum Questions Oh - just one follow-up if you don't mind. If I do a plenum, whether in the sump or the main tank, should the upper layer of sand be the fine oolitic stuff or the more coarse aragonite reef sand stuff?  <The finer oolithic stuff is better> Most of the pundits out there seem to recommend the latter, but I can get my hands on the former for VERY cheap (thanks to Home Depot and their Southdown Tropical Play sand). Thanks again, Joe <Yes... all the way around. Bob Fenner>

Plenum install to existing setup Hi Robert, <Steven Pro this evening.> Thanks for the extremely helpful site. I have a 55 gallon tank, with fish & coral. For filtering I use LR and a canister filter. I also have a 3-5 inch DSB (crushed coral 3-5mm). <This really is not a DSB, Deep Sand Bed, because you are missing the sand part. What you have is a deep bed of crushed coral and IME/O a recipe for a disaster. Crushed coral has far too large a particle size allowing detritus, dirt, uneaten food, etc. to work its way down into the bed. This will fuel depressed pH and because it will operate largely aerobic, do nothing for denitrification.> Due to high nitrates I change approximately 100% of the water each month. I have read through the FAQ section on plenums. This looks like a good option for reducing nitrates. <As would a true DSB.> I have a few of questions: 1) Should the canister filter keep running during the setup. <Yes, because this may make up a significant portion of your biological filtration. Your crushed coral is working somewhat in this regards and until your new sand is cycled you will need the additional filtration. Better to not change too much at once.> 2) How long will it take to notice a reduction in nitrate <No telling, depends on husbandry, bioload, source water, ...> & will there be any other chemical changes. <Increased buffering, pH stability, and additional calcium> My LFS says there is potential for huge increase in phosphates. <Bogus> 3) I was thinking of installing the plenum in half the tank to see how this goes and then extending to the other half. Are there any problems with doing this? <I would rather see you buy completely into one method and hold true to its design/ideology.> 4) After the plenum is setup should the sand be left alone or sifted? <If inoculated with plenty of critters and your tank does not have too many predators, there should be no need.> Regards, Michael <Have a nice night. -Steven Pro>

Re: Plenum install to existing setup Thanks for your quick reply Steve. Can I just clarify: Do I need to add sand to get anaerobic conditions? <Yes> If I keep an approximate 5 inch bed how much should be sand/how much should be crushed coral? <If you go with the plenum system, there will be two layers, about 50% each.> How fine should the sand be? <Sugar fine for the upper half> Should the sand be above/below the coral? <Above the crushed coral> Can I add and not use a plenum? <If you add a plenum it is being used. It is nothing more than a physical barrier. Perhaps you should search out the works of Dr. Jean Jaubert, the "inventor" of the plenum methodology.> Thanks, Michael
<You are welcome. -Steven Pro>

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