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FAQs about Marine Substrates: Depth  

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, Coral Sands, Silicates, Dolomites/TapAShell, Southdown & Such, Collecting Your Own, & Physical Make-up, Size/Grade, Location, Marine Substrate Cleaning 1, Marine Substrate Cleaning 2, Moving/Replacing/Adding To, Marine Substrate Moving/Replacing/Adding To 2, Substrate Anomalies/Trouble-Fixing,


Shallow sand bed questions      3/7/17
Dear WWM Crew,
<Hey Rick>
I have been reading all of the information on WWM articles and FAQs related to shallow sandbeds, and reviewing my copy of Conscientious Marine Aquarist, but am a little confused in a couple of areas. My experience has all been with DSBs in larger tanks, so going with a SSB is a bit new to me.
<There are reasons, and proponent of both; and none! Shallow ones look better than naught, but are easier to keep clean; do provide some additional alkalinity and alkaline earth materials, substrate for habitat/organisms...>

Here's the description of a new 60 gallon cube I am setting up for my wife. It will have a good amount of water movement with an Eshopps RS-100 sump, Reef Octopus 110INT skimmer, Sicce 4.0 return pump running at about 650 gph at the tank's head height, two Jebo PP4 programmable wavemakers (132-1850 gph) , and an MJ1200 pump feeding a mixed carbon/gfo reactor.
There'll also be an ATO added. She wants a shallow sandbed so planning 3/4 inches of CaribSea Special Reef Sand. The lighting is an Aqua Illumination Hydra 26HD mounted 8 inches AWL. Salt mix will be Instant Ocean Reef Crystals. Water changes and will be 10% weekly, including vacuuming half of the sandbed each week.
<A good regimen>
Livestock will be more towards corals with a medium population. Estimated total water volume after sand and rock is about 70-74 gallons.
My first question is on the amount of live rock recommended when running a shallow sandbed. I have always used the "1 to 1.5 pound-per gallon"' rule, but reading a lot and hearing at LFS that the current recommendations are for less rock, using around 3/4 to 2/3 pounds per gallon rule.
<Am more of a fan of this latter; and the use of less-dense (S. Pacific) rock. Bommies not walls is a motto>
Since my understanding is live rock has limited ability to reduce nitrates, what, if any, impact does the sandbed depth have on the amount of live rock to use?
<Mmmm; both aid in denitrification and interstitial fauna (food et al. organisms) production... Depending on composition and surface area both add the aforementioned chemical help>
Do you feel 40-45 pounds of rock is enough for his tank or is more recommended. I am using mostly Fiji live rock.
<This amount is fine. Try it and see; you can add more later if you want>
My other question is on the cleaner crew to add in a few weeks. I'm thinking of going with a couple of Sally Lightfoot crabs, a mix of smaller snails (mostly Nassarius, Ceriths and bumble bee) but beyond that unsure what to add.,
<Meh; am not a fan of crabs really; and just a few snails...>
My wife's heart is set on adding a goby and Peppermint or cleaner shrimps. But with a SSB I am concerned about starvation for them.
Any recommendation on mix and numbers for a cleaner crew?
<Naught more than we have archived on WWM; really>
Thank you for all of your help and all you do for our hobby!
Rick Morris
Dacula, GA.
<A pleasure to share; aid your efforts. Bob Fenner>

Substrate depth, SW, NO3, rdg.     9/12/13
Morning crew
I have been fighting the nitrate battle for a number of months now and have utilized a number of methods in effort to control (Vodka being the most effective however have recently taken this offline and am trying the Aquaripure).
<Have you read here?:
and the linked files above?
 I recently ran into a fellow enthusiast who ran nothing on this tank other than a protein skimmer and a couple of power heads and his water was pristine. His thoughts to me was that my 3" deep aragonite bed is the primary cause of the high nitrate issues and that I should reduce the entire bed down to approx. 3/4".
<A possibility... See WWM re substrate depth for marine systems... There are several references to this situation>
 If this is what I should do, is there any way that I can save all of the narcissus snails that are in it along with the smaller starfish that come out at night.
<You could "hand sift" much of the aragonite, saving many of these animals.
Another possibility is simply to add more fine material amongst the aragonite. READ here:
Scroll down to Mar. Substrates...>
 I have had the aragonite in my tank for almost 2.5 years so it's undoubtedly time to do something. I just want to make sure that what I do will be the most effective in the long term.
Let me know..thx Chris
<Read on! Bob Fenner>

Sand bed... input re depth, SW  12/5/07 Hello I've read through the FAQs on sand beds (it's taken me nearly a whole work day) and the majority of you guys seem to be in favour of having either a half inch substrate or more than 4 inches. <Yes> Then again, there are some who seem to like 3 inches. What everyone seems to have overlooked is the reasons why. <Mmm, these speculations/assertions are posted as well...> There is no clear explanation anywhere. <The thought is that avoiding intermediate depths to stave off the negative effects of trapped material, an-hyp-oxia... and the resultant metabolites of low/no oxygen decomposition thereof> The reason I wanted to know this is because I have a 2-3 inch sandbed (running for 2 years) and have had zero problems with it. <Easily done... the "rule of thumb" depth statement/s are just that... depending... on the actual physical and chemical make-up of substrate, the particulars of the individual hobbyist maintenance, foods, feeding, circulation... many other factors... any depth of substrate may be fine to fantastic...> My nitrates are always zero. The sand is almost always beautiful white; where other tanks I've seen (including the LFS tanks) have deeper Sandbeds which are just plain eyesores due to the amount of BGA growing all over them. My substrate puts them to shame. Also it would seem like you dislike cleaning the substrate. Well the only problem I've had with mine is the occasional diatom patch, and what I do, will likely shock you, but it works a treat. I siphon this sand patch out and repeatedly rinse it with fresh tap water! Once again, no problems at all. I just wonder if people are being led astray? Or have I just been lucky? Please explain. Thanks. <Thanks for your input. Bob Fenner>

Which Marine Substrate?...How Much? - 01/26/07 Hi Bob/staff...greetings Crew. <<Hello>> I have a 29-gallon system, with BakPak skimmer, 10-gallon sump, and # 30 LR.  My tank has been running bare bottom for a few months now.  At first it stayed clean, but now there is still some algae and the corals don't look as good as they used to.  My mushrooms don't expand well and Zoas have been strangely melting down suddenly. <<Mmm, likely deteriorating water quality/buildup of nitrogenous compounds.  Stepping up water changes and employing some chemical filtration (carbon/Poly-Filter) should help>> I want to have a sand bed; I hate the way bare bottomed tanks look. <<Me too>> Can you please share your opinions on substrates, and what you think will do well in my system, (grain size of sand, depth of the sand bed, live rock placement) and ways of keeping the sand clean and the tank healthy. <<Many opinions to found on this...but for me, a sugar-fine aragonite substrate of about four-inches in depth would be my choice here.  Utilizing strong/robust water flow will help keep detritus in suspension and out of the sand bed.  Do have a look here and among the associated links at the top of the page: http://www.wetwebmedia.com/marsubstr.htm Thanks for any help. <<Happy to assist, EricR>>

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>

Substrate Questions Hi again, and thanks for the excellent advice as usual! I have another question about the type of substrate to use for my new 180 gallon fish only tank. I prefer to use a very thin layer of sand grade for the substrate instead of a course coral substrate based mostly on what I was reading in the WWM FAQ's. I noticed someone stated course substrate is harder to maintain, more detritus and "bugs" can develop in the substrate. Is this true? <All three are true, the first two are disadvantages, the last part about bugs is a good thing.> I was told be someone else not to use sand for a fish only tank, not sure exactly why. <Bare bottom tanks are very easy to clean, but can be ugly.> I have a good protein skimmer, (DAS BX-1) and it appears to be working fine now on my smaller tank in keeping the nitrates down, (around 15-20p) . My intent is to keep the nitrates really low and eliminate much of the extra debris / detritus that develops on the bottom of the tank. If sand is ok, how deep should the bed be? <For good denitrification and no settled detritus, use a 4" sand bed of fine sugar size aragonite.> Any suggestions would be great! <Have a nice night. -Steven Pro>

One more add on question (marine substrate depth...) What is the depth of sand substrate you recommend?? With our sixty lbs of bioactive aragonite reef sand we have about 1 inch. Should we add more??? <Less than 1" or greater than 4".> We're planning on a fish and invert. system and our next addition will be live rock in a few days/weeks. Again, thanks again for your help!! Katie <You are welcome. -Steven Pro>

Substrate question <Anthony Calfo> ok - question, the recommended sand bed for denitrification is 3-4". Otherwise keep it shallow to prevent Hydrogen Sulfide release. This is usually using CaribSea Seaflor type of products. However, using the super fine (0.2-1.0m) grain Aragamax they claim that de-nitrification can occur using 1" floors.  <I couldn't disagree anymore with that statement> For safety sake, lets say 2". Is this a safe route to go about building a sandbed using Aragamax at 2" rather than 4 ? <Their argument is particularly ironic and funny that they only need 1" compared to 4" when all of the aragonite mined for our industry come the same single source (formerly Marcona Industries)...hehe. You just have to love a multi-million dollar industry without consumer watchdogs... I love this country!> I'm not quite willing to go 4" on an 18" tank, but 2" is reasonable ? otherwise, I'll stay shallow at 0.5" or so. <.5 and water changes it is> The other question is, with this fine sand, will it harden and make the lower areas hypoxic rather than anaerobic ? I've been told with non-reef based tank (basically no Kalkwasser), that this will probably not be a problem. <agreed...but, Kalkwasser is not the problem... Misapplied Kalkwasser is the problem with clumping> I imagine the sand sifting organism (hermits, crabs, gobies) will keep sift through it even though it packs down a bit. Any thoughts on using a shallower sand bed (2") with the much finer grain products ? <same as before and before.... 1/2 inch or less... 3+" or more... no in between> Thanks Ed <Anthony>

Sand bed Hello All: <Scott> I am considering changing my sand bed from a plenum to a sugar grain DSB. I would like to just add the sugar grain size sand to the existing bed but I am worried about an anoxic situation that will produce sulfur dioxide?  <Maybe... but not if the system is otherwise managed properly> I am worried about a nutrient sink with the grain size specific to a plenum. Maybe I should leave well enough alone! Thanks Scott <Maybe. Plenty on plenums, substrates archived on our site: http://www.wetwebmedia.com/ Bob Fenner> 

DSB, etc. Hello again: <Greetings!> So, I read info on your site about LS and DSB's until I was bleary-eyed (and still have not finished). <I know that feeling as well!> I then went out and bought some Southdown Tropical Play Sand that I saw mentioned. Then I realized after putting some in, that 4" is a whopping 20% of my 55gal tank depth. WOW! <It is a trade off for everyone.> I was surprised it was so DEEEEEP. I already suffer from tank envy, and the thought of losing that much height pains me.  I read on your site that someone had a 29gal, and your crew said that they probably would not need it so deep because of the lack of size.  Is there a more accurate sand-to-depth percentage to use as a general rule that may be better? <Not that I am aware of...either very thin, like less than an inch Or deep with 3 inches on the shallow end of DSB and 4 inches + even better> maybe a surface-area-to-depth? <I've personally never heard of anything like that. DSB's are somewhat controversial, therefore opinions differ. Compare the DSB idea to the concept of a Berlin tank. They are the exact opposites yet many experts believe DSB's are the only way to go...just as many think they are just a nutrient sink. You must read/learn and decide for yourself. I had to make the same decision for my tank.> I did not catch any info on that on your site (yet).  If AQ <AQ=Aquarium?> husbandry success is truly on a case by case basis (isn't it?), <Quite frankly, people that are serious enough to read/learn about water management, disease, stocking, etc. and buy a few books will be successful in this hobby. It is the people that buy a tank, put in salt water, and start throwing in critters that leave this hobby with their wallets lighter and a chip on their shoulder. You are well on your way to being a success. Keeping learning.> How would I know without trying lesser depths that it is working or not?   <The differences will be subtle either way.> Also, I read you can siphon out your old CC substrate instead of the messy way. <Not if the CC is really big pieces. Small pieces the size of  freshwater gravel will siphon out easily. Just get a cheap gravel vacuum and hose from any good fish store. Buy the largest size you can find.> Is this by using gravity alone? <Yes!> What thickness of tubing would I need?  <See above.>   Thanks for your helping "the new guy". <Don't worry my friend. All of us were new once! There a lots of differing opinions in this hobby. You need to read everything available and then decide what makes since for your aquarium. You're on the right track! Knowledge is power! David D.>

Substrate for big Australian tank and Seagrasses Hi Anthony <cheers, mate!> I'd like your advice on suitable substrate/s for our 600,000L display tank,  <glad to share an opinion> remembering that the water depth will be six meters and the habitats we're to show are sand, coral, seagrass and rock. In Shark Bay there is a small bivalve (Fragum erugatum) which proliferates in the hypersaline areas to the extent where its empty shells are harvested and sold in large quantities. The processed shells are typically 8mm diameter, hard, white and I assume composed of calcium carbonate. <yes... some form of calcite> Recently the processors have been crushing this shell to a 1mm to 2mm grain size and selling it as an aquarium substrate. I was thinking of using the same crushed substrate in our tank for the "sand" and some of the "coral" sections. How thick should I make it here?  <that depends on your intent and to some extent the livestock. If you have no other means of denitrification and will consider a deep sand bed methodology in the display proper, then we need 15-30 cm bare minimum. And in such a large display... I really must say that 30-60 cm would be quite nice. The advantage is that it will provide natural plankton (nanoplankton, bacteria etc) and naturally denitrify will little support. The disadvantage is that it could be a liability with inadequate water flow and become a nutrient sick and support dreadful nuisance algae. Nuisance algae could be further mitigated if the material is rich in silica, which as a mollusk it is quite possibly so. My advice is to get a assay of the materials composition and compare it to a known "safe" substrate commonly used by aquarists or public aquaria. That will tell us first if we can even continue to consider these crushed shell as a candidate> Do you think this substrate would also suit the "seagrass" section, or would it need to be finer than this?  <I must admit... I am somewhat concerned that this is a little too course for seagrasses and good denitrification (if the bed is shallow). Here in America, we commonly culture Thalassia and Syringodium (some Zostera too) in muddy fine substrates ranging from .2 to .5 mm> I would like to grow local species of seagrass and notice that the natural substrate is a lot finer than this, and more silicon-based rather than CaCO3.  <interesting about the silica. I'm not sure if it is utilized or simply tolerated by the grasses though. Still... if the course media is to work at all... I am sure the grasses will need to be planted rather deep... 8cm minimum.> Would I be better off using the same substrate as found in the bay, or would this silicon-sand be likely to encourage diatom blooms?  <indeed... I'm concerned about excess silica in a closed system where large water changes are not convenient if necessary> Perhaps I could have some of the shell substrate crushed a bit finer if this is important for seagrass.  <if possible that might be ideal. Do know too that the dry substrate will need to age for some months before it can support the seagrasses. When you collect the grasses, you will need to collect them like plugs (large cored berths) if you are to have any chance of successfully transplanting them. Perhaps you can just take a little extra natural substrate with you and seed the dry crushed shell in those few spots where grasses are planted early while we are waiting for the rest of the bed to mature and the grasses to spread>  I notice many seagrass species have roots that penetrate at least 300mm into the sand. Should I make our substrate in the "seagrass" section this deep?  <it does not have to be quite this deep in my opinion... but they do need deep beds and anoxic conditions. Hence the need for deeper substrates if you use courser media (the course media allows better/unwanted penetration of oxygen rich water)> Is it possible to have the substrate too deep? <not likely at all... if you said you wanted it 90cm deep, I would have no complaints!> One other thing I have noticed is that the sand in the bay seems to be quite nutrient-rich - when you dig down 100mm or so it becomes a grey color rather than white and smells rather organic. Do seagrass species use nutrients in the soil for growth, or are the nutrients obtained from the water as for other marine plants?  <they derive nutrients from roots, stems and leaves... but a rich substrate is quite important> If the soil is a major source of nutrients, do I have to enrich my substrate before it will support seagrass? <yes... recommended here as per above with this soil buried in little pockets where you first transplant seagrass plugs> Our construction is still going forward, although rather slowly.  <all in good time... like fine Australian wine :) Ahhh... if only I were sipping Shiraz/Sirah right now!> At least six months until we can put water in it. Gives me plenty of time to learn all these important things :) I'll send more photos when the tank is at full height. <excellent, my friend. I'm looking forward to it!> Thanks again Pete McKenzie <Pete, do look over these links for advise on transplanting seagrasses. Some very good information on harvesting and transplanting techniques. http://chl.wes.army.mil/library/publications/chetn/pdf/cetn-v19.pdf and here: http://chl.wes.army.mil/library/publications/chetn/pdf/cetn-v11.pdf With kind regards, Anthony>

Substrate depth on new tank Hi guys, <Hi Greg, Don here today> I have a quick question regarding Marine Substrate? I've got a 55 gallon tank with about 45lbs. of live rock and about a 2" layer of Aragonite across the bottom. Is this too much? Is it too late to remove some of the sand? The tank has been cycling for about 2 weeks now. Also, would it be beneficial to place the live rocks on some eggcrate? Thanks in advance. <Well the recommendation is for less than 1" or more that 4". You do not say what the end game is here so some assumptions have been made. Since the tank is brand new, I think I would remove some substrate and try to sell it to a fish buddy, or save it to replace your substrate down the road (store dry and as air tight as possible). This may add a week or so to the cycle process, but remember: good things are worth waiting for. I do not believe it is necessary to put the rock on eggcrate for long term. Don> Regards, Greg

Sand beds Hi, I wonder if you could refer this email to Anthony.  Hi Anthony, how have you been?   <keeping busy my friend> I just moved my 90G FOWLR to the basement and will be moving my 125G Reef this weekend.  I belong to MAST and MASK (Marine aquarium society of Toronto and Kitchener respectively).  At our meeting last night, a good friend who has recently been introduced to your book, advised me that my 3" sand bed is not a good idea and I should change this during the move.  He referred me to page 94, and sure enough you recommendation is 1/2" or 5-6", nothing really in between.   <the meat of the matter is that the advice given is geared to the masses. Actually, sand can be maintained successfully at any depth. Most aquarists though have inadequate water flow, overfed or overstocked systems and need denitrification. As such, a deep sand bed (DSB) will support this inevitable reality or... the shallow bed will not amplify it problematically. The concern with in between (1-3" depth) is that it is neither deep enough for adequate anoxic faculties nor shallow enough for efficacy aerobic faculties. You still make in into the recommended range of 3" or more that the industry commonly cites as a bare minimum for NNR (natural nitrate reduction). My advice for the extra sand prevents the need for you to add sand frequently to stay above 3" for NNR> My reef is 5 1/2 years old and I can't say I have had any issues (probably luck?).   <not luck at all my friend... if your nitrates are near zero, I'd say it has simply been good husbandry on your part> So my question, should I either remove the Aragonite to 1/2" levels or increase to the 5-6"?   <May be very fine as it is. If you have any concern about present or future nitrate accumulation (desire for more fishes, extra feeding, growing corals, adding corals, etc), then perhaps extra sand will be helpful to you> As the tank will have to be emptied this is the ideal time to make a change. <agreed> Thanks for all your help in the past, BTW tank parameters are all fine!  Larry <excellent to hear! Best regards, Anthony>

New tank...need advice Dear Bob, I visited your website and I found it the most useful marine site out of the dozens or so I'd encountered. I currently have a AGA 72-gallon bow front aquarium. I'm planning to set-up a reef tank with soft corals with various invertebrates and fish. However I need some advice on the equipments I will need in order to make this system successful. I plan to use Instant Ocean Sea Salt and lay 40 pounds of Carib-Sea Live Aragonite Sand (1-2mm) on the bottom of the tank (hopefully this will be about 1-2 inches).  <40 lbs of sand will barely make an inch, in that tank. Personally, I'd mix the live sand with the finest aragonite (dry, but carefully rinsed) that you can find, if you're looking to save a few dollars. But the trade-off is that rinsing the dust out of bagged aragonite is agonizingly tedious...and you won't have to do that with the live sand.> I have a Hagen Fluval 404 canister filter, Hagen Aquaclear 300 power filter, Hagen 200 watt Tronic-Electronic heater, AGA twin tube light hood, CustomSeaLife PC Hood(110 watts) w/ 2 SmartLights, and I'm planning to buy a CPR Bak Pak 2 protein skimmer.  <Those should cover you fine, if you're careful to let the tank cycle slowly and completely, before you start stocking like crazy...> I also plan to buy a mixture of live rock mixed with Tufa rock, with Tufa rock being more abundant as I'm on a tight budget.  <That's fine. Again, go slow with the stocking plan. Within months, your Tufa will start to look more and more like your expensive live rock, and in a couple years, you can't tell the difference.> In addition I don't exactly know how many powerheads I should use and at what rate each of them should be at. What brand of powerhead would you suggest?  <I like to use 4 power heads in a 48" tank, at each end, pointing toward the middle. I tend to use RIO 800 or similar for that application, but the Rios are starting to get on my nerves. Replacing suction cups every few months...> Can you please tell me if I have adequate equipment for the system to work and any additional information or advice? Thank you so much!!!! P.S. How should I clean the Tufa rock and about how long would I need to cycle my tank before adding any livestock? Thanks for your help!!!!!!!!!!!! <You can just rinse the Tufa real well with hot-hot water in the shower or bathtub, some folks (obsessive?) will go so far as to boil it. Not me. As far as cycling/setup, I'd let the tank sit with the filtration and substrate for 24 hours, then with the Tufa for 24 hours, then start adding live rock (I don't like to add more than about 20 pounds every 24 hours). Then a couple small fish, for 2-3 weeks, with testing for ammonia/nitrite/nitrate, to observe the actual cycle. Don't put your 'show' fish in there for at least 4 weeks from day one, if you can hold out! -Lorenzo> Peter

Re: Substrate Question Thanks for the quick response. I was jumping up and down in excitement when I actually received an answer from you. You are the man! <The petfish man!> A local fish store here sells a sugar-size aragonite. Do you recommend this, or should I go with bigger size grains?  <For some applications yes... but not for a general tank bottom> Which type of substrate would you recommend if not aragonite? <For most types of tanks something calcareous... Hey, I should be sending you to the "marine substrate" section of the site: www.WetWebMedia.com under the marine index... wrote, stored my ideas on the topic during some few lucid moments... let me know what you think of the site>  Thanks again. Sincerely, Aldrin
<Be chatting, Bob Fenner>

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