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FAQs about Marine Substrates: Coral Based

Related Articles: Marine System Substrates (Gravels, Sands) by Bob Fenner, Marine Substrate Options by Sara Mavinkurve, Deep Sand Beds, Live Sand, Biofiltration, Denitrification, Live Sand, Live Rock, Biominerals in Seawater, Understanding Calcium & Alkalinity

Related FAQs: Marine Substrates 1, Marine Substrates 2, Marine Substrates 3, Marine Substrates 4, Marine Substrates 5, Marine Substrates 6, Marine Substrates 7, Marine Substrates 8, Marine Substrates 9, Rationale, Selection, Reef  Substrates, By Type: Aragonite/s, Silicates, Dolomites/TapAShell, Southdown & Such, Collecting Your Own, & Physical Make-up, Size/Grade, Location, Depth, Marine Substrate Cleaning 1, Marine Substrate Cleaning 2, Moving/Replacing/Adding To, Marine Substrate Moving/Replacing/Adding To 2, Substrate Anomalies/Trouble-Fixing,

Coral sands, yay! Crushed coral, boo!


Crushed coral giving me a headache, 12/21/11
Hey guys / gals at WWM.  Firstly I'd like to thank you all for so selflessly devoting your time to help those in the hobby, its such a great and interesting resource I have trouble getting any work done! (I'm working now ha)
<What is this work thing you refer to?>
I have a 3 foot LPS tank for over a year now but I have a bit of an issue developing.  I would really appreciate some expert advice re my 1-2 inch crushed coral substrate. Unfortunately its gradually becoming more and more dirty looking (see att.), despite siphoning it weekly with water changes and stirring it up now and then. I'm afraid it is turning into a detritus sink.
<That is the problem with it.>
I'm wondering instead of removing it, could I just cover it with 2-3 inches of a sugar fine substrate like aragonite? Or is that like brushing rubbish under a rug?
<Pretty much, and the sand being more dense will eventually sink below the crushed coral so it really won't fix your problem.>
I'm concerned that in removing it there will be a collapse, as my rock and corals aren't glued (also attached) and also that the bacteria loss with the substrate may cause a nitrite spike. Unfortunately I can't go back in time (yet) so what you recommend? Cover it up or replace it completely?
<Replace unfortunately, otherwise you will just have more problems.  Long term replacing it will be less work, but it won't be fun to replace.>

Re: Crushed coral giving me a headache 12/22/11
Cheers for the quick reply, even if it wasn't what I wanted to hear.
<No problem, sorry I had to be the bearer of bad news.>

Sand or crushed coral, maybe both? 8/8/06 Hi, <Hello> I have a 55 Gallon fowler tank. Not much in it right now,50 pounds live rock, 3 turbo's,6 red and blue leg hermits,3 Astraea snails and 1 clown. The tank has been set up now for about 3to4 months. My sand bed is made up of 30lbs Aragamax sugar sized sand mixed with 20lbs live sand. <How deep is it?  I'm guessing 2+ inches.> My problem is that the sand gets so dirty looking (brown algae and snail poop I think)  when I try to clean it the sand gets EVERY where by the time it settles my live rock is just covered and looks like crap. I hear good things about sand helping to control nitrates, that's why I went that way. <At the right depth it can be quite useful for nitrate reduction, 3+ inches at least.> But I was wanting to maybe go the crushed coral route. <Can be problematic, trapping detritus.>  I don't know any body that has a saltwater tank and the LFS in my area are not worth going to "they don't even sell RO water" so I thought I would ask some one who could help me out a little!! <Hopefully> Should I try the coral or stick with the sand? <I prefer sand, either under 1 inch or over 3.>  Can you mix the two and have the coral for the top layer? <Worst of both worlds, I wouldn't recommend it.>  Is the coral easier to keep clean? <Not really.>  Also one more question I did some reading just incase I did go with the coral about keeping nitrates down and I came across a DIY project called a coil denitrator that claimed after two months of cycling it will help keep nitrates down ever heard of anything like this? <Yes> Maybe worth trying? <Lots of work, mixed results at best.  Water changes and a deep sand bed are easier in my opinion.  Give this a read for more http://www.wetwebmedia.com/deepsandbeds.htm > Thanks for any help Brian <Anytime> <Chris>        

Crushed Coral Substrate  9/13/05 Hey guys, hope you're doing well tonight.  I want to thank you once again for preventing my tank from becoming a 1,000 pound paperweight. <Many of them out there> Anyhow, onto the question of the day.  I have a 100g reef tank with a crushed coral substrate.  I know that crushed coral is notorious for trapping detritus, but I was wondering that if the substrate has noticeable amounts of amphipods running around, along with bristleworms and a whole host of other things when the lights go out, is crushed coral still good or is it just too much of a nitrate magnet.   More to the point, with the increase in detritivores (and regular water changes) will nitrates ever become an issue.  I'm loathe to vacuum the substrate because I know I'm pulling out tons of little creatures each time I do.  Any help would be appreciated. <Clay, nitrates develop from high detritus levels resulting from uneaten food, fish waste, etc.  In your case the critters in the substrate are helping in reducing the waste.  You didn't mention your last nitrate reading.  If it is 20 or lower you should be OK.  You didn't mention the use of a protein skimmer.  These will also help lower nitrate levels to acceptable levels.  Search our WWM, keyword, "nitrate control" and read on this subject for additional help.  James (Salty Dog)>

Curing Live rock and crushed coral in a reef 7/29/05 Hello Crew, <Howdy Frank! Ali here...> Thank you for all for the effort that you put into this wonderful website! <Merci> What a wealth of knowledge! I have a quick question about live rock and substrate. I have a 90Gal marine aquarium with some soft corals and some fish. I started the tank with about 2" of coarse crushed coral substrate and 50 lbs or live rock. I have recently acquired another 150 lbs of live rock which I am currently curing. <Make sure you cure your rock for at minimum a full 4 weeks. Utilizing LOTS of circulation in the holding "bin" will go a long way. Additionally, it would be better to add 1/4 of your new rock per week, so that in 1 month's time all of the new rock will be added. This is AFTER the initial minimum 4 week curing phase. > The question that I have is if I add all of this live rock into my aquarium, I will be covering up a lot of the crushed coral on the bottom of my tank and will therefore be unable to vacuum most of the substrate in my tank. Is this going to be OK, or is it going to lead to problems in the future? Will I have to switch to a deep sand bed in order to add this rock? I am trying to do what is best for the marine life by adding the rock, I do not want to create any dangerous side effects in the process. <Generally speaking, crushed coral isn't something you want to utilize in a reef aquarium. You will have less problems in the future if you bite the bullet and do a tank renovation, removing the crushed coral and replacing it with a fine grained deep sand bed 3-6" or simply going completely bare bottom, or perhaps a shallow sand bed 1-2" of fine grained sand. The CaribSea Aragamax Select sand is ideal for this and can be found at most reputable dealers.> Thank you, Frank <No problem Frank! Good luck>

Replaced Crushed Coral with Sand 10/29/04 Hello crew, kudos on your site. <Thanks!  Glad you like it.> Last week I changed out the crushed coral in my 100 gallon FOWLR with 60lbs of Fiji pink aragonite sand and 120lbs of Fiji pink Aragalive live sand. During the process I took the 120lbs of live rock out, removed the crushed coral, placed the aragonite in first then sped the live sand over the aragonite, and replaced the live rock, then I reused the water that was siphoned out of the tank. <Sounds like about the same way I would have done it.> There has been no cycle (which I didn't think there would be much one). Total depth of sand is 5" to 6" of sand in the tank, about the same in the sump (was already in the sump) and some live rock rubble in the sump with a TurboFlotor 1000 skimmer (thanks to Bob for the recommendation the skimmer it's great)<I agree that a cycle should not be expected.  The TurboFlotor is a great skimmer, but probably somewhat undersized for the tank.  If you have any nutrient issues, I would consider upgrading.> there is 500 gal. flow through the sump along with 1200 gal circulation in the tank using power heads. my main question is how long will it take for the sand to help decrease nitrates? <I would give it a couple of weeks.> Right now they're 80 on the test kit and I am doing water changes but I don't want to start a cycle in the tank with to frequent water changes (I was thinking about 20gal a week till the nitrates are under control) <I would slow down on the water changes.  There is no reason why this would initiate a cycle, but the more the bacteria are fed, the faster they will grow.  Be patient, they will come down.> oh yea there was an under gravel filter under the crushed coral (nitrate factory) which went into the trash.  Sorry about being long winded, and I read your site every day. Thanks Ed in West Texas  <The ideal place for the UGF in my opinion.  Thanks for visiting!  Adam>

UGF plate in tank to create denitrification Bob, We've spoken recently regarding my new tank set up using RUGF <Reverse Under Gravel Filtration> with Crushed coral as substrate. I'm a newbie. As I keep reading up on all this stuff it seems that denitrification is one of the hottest topics when it comes to marine tanks. My question is.......instead of my original plan of a RUGF with Crushed Coral.....if I just use an UGF plate in my 75g FOWLR w/a few Shrooms and softies, and use 1 1/2 of Crushed Coral, will it create a denitrification zone in the tank? <To some degree... would be far more effective with a deeper substrate level, depending on grade, three, four inches> And would regular aragonite sand be better vs. the crushed coral? <Of same average diameter, no> I'm not sure I know the difference between the two (CC vs. Aragonite) other than one is a larger size than the other but they have the same chemical make up. <Actually... aragonite/s are mined, consistent composition... calcium carbonate... crushed corals are collected inorganic matrices of organic origin that contain considerable "impurities" of use... like magnesium.>   I'm reading where CC seems to be a substrate that buffers well and holds the ph constant among other things. What do you think about denitrator units?   <... am a big fan. Bob Fenner> Thanks Don

Setting up a 135 Hello all. How are you all doin?  Good I hope, I'm good myself and excited. We just set up our 135 reef, got the sand and water in and are now going to Vancouver B.C. to get all our supplies. You guys have helped me with all my countless emails and I really appreciate it and just wanted to say thanks. Now one last question (there's always a catch) Here's my question. I have a 40 gallon sump and am wondering what substrate to put in? I don't want to put sugar sized for the fear of it getting blown around, would Florida crushed coral work? << Crushed coral is my favorite. >> I would like to have about 5 inches would this Function as a NNR? << Sounds good. >> Also I have 400 watts of PC lighting do you think this will work for some of the lower light LPS? The tank is 18 inches high << I do think it will work.  That is a lot of pc, I'd consider switching lights out, but if you already have that many pc bulbs then just keep them. >> Thanks a lot Sharon <<  Blundell  >>

Crushing crushed coral Hi WWM crew. <Stephan> I have some crushed coral about 10mm from my former tank and I want to put it to good use for a refugium. Can This stuff be reduced to a powder and how would you crush it asides from renting a steam roller? Thank a bunch for the continuous help. Stephan Gaudreau <Could be crushed by some gear... or taken to a hobby, jewelry making shop... to crush, then screen/sort... but for the cost, trouble, I'd buy some fine material and maybe mix it in with some of this larger grade coral substrate. Bob Fenner>

Thermometers & Substrate I have 2 questions for you all today 1. which is better as far as thermometers go the glass ones that go inside the tank or the sticky ones that go on the outside? <IMO, the glass ones are better, but should not be allowed to float around in the tank waiting to get broken.> 2. When I bought my substrate (crushed coral) the guy at Elmer's LFS said NOT to rinse it, but the bags say to do a light rinse. <Crushed coral needs rinsed like crazy.> Which is right? <Are you sure you have crushed coral though. Being from Pittsburgh and knowing Elmer's, I am not sure they carry crushed coral anymore. They do have various grades of sand, some larger than others.> It is not live sand. Thanks, Colleen Pittsburgh, PA <By the way, did you make Bob's pitch at Elmer's on Saturday morning? -Steven Pro>

To Rinse or not to Rinse III Ok I'm home now have set up the tank did rinse the substrate and the bags did say "aragonite grade crushed coral" there is like tiny shells and stuff in it. Not sand for sure. With three bags the base is about 1" in my 75 gal tank. Everything is up and running figure I'll let it go till tomorrow and take more salt readings and pH and then decide what I'm going to do next a little damsel or 2 or just some live rock not really sure yet. ~Colleen <I would strongly suggest the live rock cycling method. You can read more about this on WWM. -Steven Pro>

Non-sand bed thickness ?? I have a 29 gal salt aquarium with ~ 3 inches of crushed Florida coral.  <Yikes!!! A scary detritus trap... any dreadful algae growth in the tank because of this nutrient sink?> Most of the pieces I can see are fairly large coral or whole snail shells that average 1/8" to 1/4" across. I have read on some of your other FAQs that using between 1-4 inches of sand bed depth may cause long-term problems. Is this also true of the coarser substrates like mine? <especially true of coarse substrates!> I would also like to adapt my substrate for NNR. Would adding 1-2 inches of fine aragonite substrate work with the existing crushed coral underneath, or should I look at replacing the CC.  <alas... mixed grain sizes are problematic. NNR with a deep bed of sugar fine sand. 5+inches gets my vote> BTW, I just started a 10 gal refugium with 20 lbs of live sand, 3 lbs of live sump rock, and some Caulerpa. Is it still worth the effort/expense of trying to set up NNR in my main tank's substrate? <likely yes... most display tank bio-loads can burden a 10 gallon refugium no matter how efficient it is> Thanks, Darrell <Always welcome my friend. Anthony Calfo>

How much crushed coral? Hi Bob, <Steven Pro in this evening.> I am addicted to this site. I can't get enough! The more I read the more questions I have. My latest question is in regard to the substrate. I have a 20gal tall FO salt tank and I am slowly converting to more inverts. I have a Fluval 204 with carbon, power head for water movement and adding a Prizm skimmer. The first thing I want to do is add LR. I am going to be adding about 5lbs a week with a total of about 20lbs. Is this ok? <As long as it is fully cured, it is ok. Do not trust any mail-order liverock as being fully cured. Archive the WWM site on liverock for additional info.> Also I have about 3 inches of fine crushed coral as a bio bed with nothing underneath. I was thinking of taking it down to about 1 inch and relying on the LR for most of the bio filtration. I figured with less substrate the easier to keep clean and less likely for waste to gather. I want to be able to set up my LR so I don't have to do much moving when cleaning the substrate. What do you think? -Shaun Nelson <I would take the crushed coral down even farther, to perhaps 1/2". A thin layer of crushed coral is good for pods, but does tend to collect detritus. You may want to raise your liverock up off of the substrate by using sections of PVC pipe or lift-tubes or something else to allow for easy of water movement and cleaning. -Steven Pro>

CLEANING CRUSHED CORAL SUBSTRATE!!!! Dear Robert, <Steven Pro this evening.> I'm so glad I found your site. I hope you can help me with my new cichlid tank set up. Though I cleaned 40 lbs. of crushed coral the best I could, once it was in my tank with water (46 gallon) it still seems to be very dirty as the tank has been white and cloudy for a couple of days and each time I move around the substrate, it kicks up more and more white dust to cloud the tank. I have an Eheim canister filter attached #2217 and am using a Power Clear power head #402 for water movement.. Is the clouding eventually going to go away? <Yes> Is it normal to have the substrate give off a white cloudy mix every time I move it around? <Very normal to have cloudiness with crushed coral.> Should I simply try not to disturb the crushed coral? <Eventually it will settle down, get trapped in your filters, and removed with water changes.> Thanks so much for your advice! Mitchell Wexler <You are welcome. -Steven Pro>

Cleaning Crushed Coral Hi crew, >>Hello you. Marina tonight. >I love your site, I go cross-eyed reading all the information you have here. I have a question regarding cleaning my substrate when I do water changes. I have about 2" of Florida crushed coral in my 29g tank. I gently vacuum the bottom when doing water changes. Should I vacuum more vigorously or just lightly. >>Only as "vigorously" as is necessary to remove detritus. You cannot, and don't want to, vacuum it completely clean, as this is where your nitrifying bacteria live in their largest numbers. If you do want to be more vigorous about it, limit the area to no more than one third to one half the substrate. >I plan on changing substrates later when I change to a bigger tank (200g in about a year). Thanks for your help and keep up the good work. Larry. >>You're welcome, Marina - who loves alliterations!

LR/BioWheels, and Substrate Hello: <Hi there! Scott F. here today!> I have a 55gal FOWLR, soon to have hearty invertebrates, 40lbs. crushed coral, BakPak2R Skimmer and Emperor 400 HOT filter with dual BioWheels.  Should I remove the BioWheels, or can I keep them running?  Is it redundant with LR?  Is my filter too small to worry about them? <If I were using this type of setup- I'd keep 'em> Also, my crushed coral is a little deep in some spots (up to 4").  I am reading this can be bad.  True?  Should I remove some?  While I am at it, can I have one side of the tank crushed coral and one side LS  (for purposes of different inhabitants?)  Thanks a bunch! <All good questions. First, crushed coral can sometimes be problematic if it's too deep. Because of its larger grain size, it tends to function as a detritus trap and pack down hard over time. As far as the 50%/50% plan is concerned, I'd just go with one substrate. If it were me- I'd go with a 4" plus live sand bed. Do read about the benefits of live sand in the FAQs on wetwebmedia.com  Enjoy!>

Crushed Coral Depth? I have had my SW tank for 9 months and have been adding live rock (now 52lbs in a 55 gal tank). Reading your web site and others this past week I became concerned that my 55 lbs (Carib Sea, Florida, 5-10 mm) crushed coral substrate was too thick (approx 1.5 - 2 inches) - I am not using an UGF and the articles mentioned to keep the substrate to 0.5 - 0.75 inches in this case as it mentioned a couple of gases that can develop that are toxic to the inhabitants (fish and corals).  This morning I read an article on your site that encouraged a thick bed (see excerpt below): Substrate question I have about a 2.5 inch bed of crush coral in my 55 gallon tank. I want to add another inch of Flamingo Pink on top of the crush coral, is this OK or will it kill a lot of my biological in my crushed coral? Also would the Flamingo Pink be ok with gobies (stirrers). Thanks, Jim >> Should be okay... density, size wise of the new/old substrates... with the gobies as well... but will the two mixing together be okay with you looks wise? They will. Bob Fenner QUESTION: Can you please tell me what the best approach is as I am very confused on how thick the substrate should be. <Well, there are lots of different opinions here. The prevailing thought is that sand beds (or gravel beds) under 3 inches in depth are too deep to be fully aerobic, and too shallow to foster complete denitrification processes. With coarse substrates, such as crushed coral, there is the added concern of detritus accumulation. With proper substrate maintenance, and the possible inclusion of sandbed "stirring" animals, this type of bed can be successful...just keep an eye on things> I am also sharing the rest of my setup for any general comments/feedback: 55 gallon 52 lbs live rock and crushed coral substrate Magnum 350 Canister with 2 BioWheels (2) MaxiJet 1200 and (1) PowerSweep 228 Coralife Power Compacts 260W (Actinic and Daylight) Skimmer - Prizm Supplements: SeaChem - Calcium +3 (Saturday), Buff (Sunday), Trace (Tuesday), and Vita (Thursday) Feed only frozen foods (varied) QUESTION: SeaChem Reef Success Calcium +3 is easy to add, but is this a Calcium Chloride rather than Calcium Hydroxide?  Should this concern me enough to change this to something else (Kalkwasser, B-Ionic, Kalk, etc.)? What do you recommend? <Not familiar with this particular product, although I think SeaChem makes some excellent ones. You may want to contact them regarding the specifics of the product's application> Livestock: Rabbitfish, 2-Percula Clown, 1-Purple Firefish, and 1-4 stripe Damsel Janitors: Serpent Star, 2-Emerald and 2-Red leg Crabs, 11-Snails (Astrea, Bumble Bee, Turbo, Margarita) I will start to add coral over next few months and a Mandarin Goby in another 3- 6 months. <I'd avoid the mandarin altogether in this tank, to be perfectly honest. To many competitive feeders. Although I commend you on holding back on adding the fish until your tank is further established, I think that it's really a fish that needs a setup dedicated to its specific needs and dietary preferences (like amphipods and copepods)...> QUESTION: Any feedback you have on this setup and the direction I am going in will be greatly appreciated. <Sounds okay so far. You didn't mention anything about maintenance procedures...I'd utilize smaller (5% twice weekly) water changes in this tank, to really get to nutrients before they have the chance to accumulate and degrade the water quality. Also, you may question yourself on the use of the vitamin and trace element additions...If you are conducting regular water changes, you are usually replenishing these substances in the process. If misused, these products can lead to nuisance algae blooms. Finally, make sure that the skimmer is cranking out at least a couple of cups of dark, yucky stuff a week> Thanks for all your help - both with the questions above as well as your extremely informative web site - it is a tremendous service to the hobby! <So glad you find it useful! It's our pleasure to be here for you! Keep reading and learning, and enjoy your tank! Regards, Scott F>

Dumping the substrate Hi Bob it is me again. I recently removed my substrate from my tank and at the same time I did a water change. The reason I removed the substrate was that my water had a film on the surface. I would do water change after water change and skim the top. Nothing would get rid of this film. I added the Kent Calcium Buffer and stopped because of the film, but there was no change. Now since I removed all of the substrate my water has never been so clear. I just received the Eco System 40 last night and I installed it. According to the Eco people you do not need substrate but you and I know it serves a vital purpose. My question is if I decide to put back the substrate what type of substrate should I use to prevent this film incident to happen again. I read the info. on your website but I would like to have your professional opinion. <Hmm, the site IS my opinion, professional and otherwise... Crushed coral is about the number one winner for most types of systems... Time re-read the "Marine Substrates" section my friend. Bob Fenner> Thanks, David S. Garcia

Changing substrate & time Dear Bob, After hassling with a hair algae problem for about 1.5 years, and talking with various experts at several different locations, (you inc.) I decided to change out my substrate to a mixture of Carib-sea Aragamax and FFE live sand. After about 15 hrs. of extreme TLC and many words that are not printable, the task was completed. <I hear you> It has now been 3 weeks to the day, and the results are great. There is no re-growth of hair algae to speak of, and the 2 50 gal. cleanup crews, (thank God for turbo-grazers) <And the hair algae...> , are taking care of what is left. All my corals and other finny critters are doing fine, after what must have been a very traumatic experience for them. My question (questions) is, would this be like setting up a new tank? <Yes, in most respects> I re-used quite a bit of water from the "old" system to refill the tank after the process was complete. All the LR was scrubbed with a toothbrush to remove the nasties. How long should one be expecting to wait to see if this changeover actually worked? <You have seen it> 80 gal. tank. water parameters all good except the iodine level 0.04 ca @ 400, alk. 9-10, mg. 1300, nitrate<10ppm. Oh yeah, one more thing. I have recently been seeing where the addition of "Kalk" is not exactly the thing to do. <About time... I've been against this archaic, toxic practice from day one...> A friend of mine has been using a product called "Aragamite" from Carib-sea to do her buffering and calcium adds. What do you know about this product and it's results? <Yes... basically (pun intended) it's finely ground "old reef"... in effect, much like wave action in the wild, many calcium reactor designs... Bob Fenner> Thanx for your input, Charlie Ehlers.

Live Sand/Substrate Questions Bob, Some time ago, we discussed adding some live sand from a reef tank that is being dismantled to my 65 gallon tank that has crushed coral on the bottom. My crushed coral is about 2 years old and I get the feeling that I should be changing some of it out. WetWebMedia suggests "periodic" changing of about 1/3 of this substrate. How often is periodic?  <After a year and a half or so the first time, every six-eight months thereafter...> Should a drop in KH level be used as an indicator? <Yes> I assume new crushed coral would reduce or eliminate the need for pH buffer (baking soda, etc.). Is this true? <Along with periodic water changes will largely eliminate the need for in "non-boosted" systems... However, folks with intense lighting, a great deal of biomineralizing livestock very often find they have to augment for pH (biomineral, alkaline components)> In the message below, you suggest I consider the live sand "if it's not ages old." How old is ages? <About the same time frame... a year and a half or more...> Can I add it on top of the crushed coral? <Yes> Thanks for your help, <You're welcome. Bob Fenner> John P.S. My wife Wally and I just had a baby boy, Stephen, on the 11th. I think he's really going to like the fish tank! <Congratulations. I am sure he will.>

I have been using marine sand Hi, Well, for about a year now I have been using marine sand at the bottom of my 72 gallon all marine fish tank. Throughout the year during water changes the sand would get sucked out little by little over time or would get so cover with algae that I would remove some. So now I am left with sand barely covering the bottom of the tank. I went and got Carib Sea "Aruba Puka" and "Florida Crushed Coral," my question is how do I go about adding this to my tank without disturbing the fish or the bio system in the tank. I have four fish, a Powder Blue Tang, Emperor Angle, Hawk Fish and a Flame Angel. Any help would be greatly appreciated. >> If it were up to me... I'd gingerly rinse/wash the new substrate in freshwater, with a garden hose, swirling about ten pound batches at a time within a soap/detergent et al. free bucket... and then simply "pour in place" the new material... You can be a little more discrete, by moving the present decor over to a side at a time, as you introduce the new substrate to the other... Should be no big change in bio-cycling... Bob Fenner

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