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FAQs about Marine Substrates: Dolomites, CaCO3 and MgCO3 Composites, Shells 

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, 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,

Dolomite limestone, use as substrate  -- 07/22/08 My husband and I are in the process of setting up a 90g tank at home. We have done some research and are interested in using pulverized limestone as our sand bed. We can't find it at HD or Lowe's but we found dolomite limestone at our local garden center. Is this the same as the pulverized limestone I have seen others mention? <No. Dolomite is a different mineral in contrast to aragonite and calcite, the more common carbonate minerals that compose limestone. Dolomite is less soluble and has a significantly higher concentration of Magnesium. It also might contain potentially harmful elements it enriched through its geological history. Especially if you want to keep stony corals, I'd prefer coral sand (also known as crushed coral, aragonite sand), which might be more expensive, but safe and potentially beneficial for coral growth and stable water parameters. Unless you know exactly the composition of this specific dolomite and can determine if it is safe for aquarium use, I would not use it.> Thanks for your help. Callie. <Hope that helps. Marco.>

Oyster shell filtration 7/4/05 Dear crew, <Mark>   Thanks for all the useful information on your site.  I have started a new 46 gallon saltwater tank that has been up for 4 months. I have 2x65 pc lighting which I am going to upgrade soon. In the beginning I had  1/2 bio balls and 1/2 coral shells in my sump with live sand and macro algae.     I recently bought some oysters to eat and came up with the Idea of using the shells upside down in my sump. I double boiled them and cleaned them and began to place them upside down in my sump, using live sand in the cup of the shell. It is a big guess of course but the way the water flowed from the wavy tips of the shell into the belly of the next seemed that it would work really well. And it only took me out about 4 bucks for the shells and a meal. But now I only seem to be growing the hard green algae. I would like to have a little more of the kind a purple tang could eat, as I am going to get one when I feel my tank is ready. The rest of my set up is (1 false Perc and seabae,1 coral beauty, 1 mandarin, 1 diamond watchman goby, 10 snails, 6 hermits 30 pounds of live rock and a 200.00 skimmer.) I am also using the sump inlet area as a sort of staging area for Caulerpa and copepods I have purchased for my mandarin. Any advice? <... have used Oyster shells... fresh and processed (mainly for chicken supplement)... not very soluble useful compounds for saltwater... Coverage on how to grow purposeful macroalgae and the fish you list above is archived on WWM. Bob Fenner>

Just How Small Is This Place!? II - 04/28/05 Thanks Eric.  < Most welcome. > Also, I recently got rid of my sand substrate because it just seemed to give me problems with making parasites linger in my tank. I want to get a fine gravel type substrate. Would dolomite and crushed coral be comparable? Do they have similar benefits or is one better than the other?  < Crushed coral is the better choice, aragonite even better. > Couldn't find anything about dolomite in the FAQ'S. < I assure you this subject is well covered...a simple Google search on the words "dolomite", "crushed coral", or even "marine substrate" will yield many hits. > Thanks again. < Regards, Eric R. >

Dolomite I am not using live rock so please help. I had seen your web site. Can I put dolomite chips size 3mm instead of coral sand? Please give download. <<Greetings friend from afar. To illuminate the topic a little further, you can use dolomite as a substrate but it should be stated that it does have its limitations. Compositionally, it is calcite and does not really offer much of any support as a buffering media (until at or below a pH of 7.6 which is too low for most marine species anyway. Coral sand of aragonite composition is a much better buffer. Still, you can use the dolomite by paying slightly better attention to water quality and specifically pH parameters. There are also some minor concerns about contamination from dolomite depending on how close to the fringe of the deposit it is mined from. If you are not using a substrate filter, only use enough to barely cover the glass bottom of the tank 10-15mm. Best regards, Anthony>

- Re: FOWLR Setup - Hi Jason, <Good evening...> Thanks for speedy reply.  I just pulled this off my LFS website.  Can you comment on the suitability of shell grit at all?? <Is one of the main components of crushed coral and the like - all calcareous [containing calcium] materials.> However, it is highly recommended to use a carbonate based substrate in marine aquaria, as this helps keep the pH stable. Marble is the most readily available option. Coral sand is also a good substrate, but it can no longer be imported into Australia so is difficult to get hold of. Shell grit can also be used, but you should ensure it is very clean. <I'm not a geologist, so I can't comment on the calcium content of marble, but I'd be very dubious about the solubility of the stuff. Calcium-based sands and crushed coral readily break down over time via natural processes in a marine system, supplying trace amounts of calcium. I'd bet that the same can't be said of marble.> Thanks mate Glen <Cheers, J -- >

Tank question Good Afternoon, I looked on your site but didn't find the answer to this question. I am trying to decide on a substrate to use for my 40 gallon breeder tank for saltwater. I currently have a 20 gallon high saltwater tank that is doing really well. I have dolomite as a substrate, no live rock, 2 external aqua clear filters and an air supply. All of my levels are stable in this tank and the fish are doing quite well but I am going to a little bigger tank.  <I am glad this system has worked well for you, but I do have some suggestions. Dolomite is a poor buffer because it only dissolves at very low pH. Aragonite or coral based substrates work much better. Also, if dolomite does dissolve, it is very high in magnesium which can be a problem. Also, I always strongly recommend live rock, even for fish only systems. Power, trickle and canister filters are expensive, maintenance intensive and don't control nitrate. Live rock is also expensive, but requires little or no maintenance and controls nitrate. Also, unlike artificial or non-living decor', live rock never needs to be cleaned!> I'm seeing all of this talk about crushed coral and sand (DSB). The dolomite in my tank is working well but a lot of dirt accumulates in it. I do regular water changes once a week and siphon the gravel. I would like to possibly add sand to the tank, <My rule of thumb for sand in tanks is to use one of three options: No sand, coarse and shallow (4-5mm or larger grain size, not more than 3/4" deep), or fine and deep (1mm or smaller grain size and 3" minimum deep). All sand will trap detritus, so the idea is to be able to get it out or for the critters living in the substrate to process it. Larger grain sizes allow easy siphoning and critters to live between the grains. Fine sands allow critters to burrow and don't let detritus penetrate, giving large animals time to eat it. Deep, fine beds of sand also are capable of processing huge amounts of nitrate. Grain sizes from about 1-4mm are the worst of all worlds... they are hard to vacuum and very few critters are able to live in it. Whatever you choose, I would recommend that you use at least 50% aragonite or coral based substrate.> but I am not interested in having live rock in my tank. I had a 55 gallon before and all of the bugs were horrible and overrunning my tank with live rock, especially the bristle worms. They were everywhere and even in my filters. Once we broke down that tank and sold it, I found a bristle worm that was close to 6 inches long. I can only imagine how long it would have been stretched out. NICE!!!!! NOT!!!! That freaking sucker hurts when they get you!!!!!!  <I understand some peoples aversion to bugs and worms, but I am such a fan of these animals, I feel like you just insulted my mother! All of these "bugs and worms" were cleaning your aquarium for you! Bristleworms are generally harmless, and only occur in large numbers when the system is overfed and/or allows detritus to accumulate. Properly fed systems with strong water movement and an occasional "rock dusting" rarely have large numbers of bristle worms. I strongly encourage you to consider live rock and the free labor force that comes with it!><<Mmm, RMF disagrees, as will anyone who has been stuck but good by some of these Fireworms... their notopodia can have very sharp elements indeed>> Anyway, could I still have sand in my 40 gallon tank without the creepy crawly things? I just want fish and a nice looking tank. Would I be able to go into the tank for the water changes and stir up the sand a bit to clean it???? What would you suggest??? Or should I just go with the crushed coral and stick to my weekly water changes and siphoning for the new tank????  <My suggestion is to welcome the creepy crawly things! However, if you just can't do it, I would suggest a thin layer of coarse Aragonite or crushed coral substrate that gets vacuumed often. This will give you the aesthetics and allow you to remove wastes.> I know that live rock is a good thing, or so they say, but after my bug experience, I want no parts of it ever again. Thank you very much for your time. Your website is terrific!!!! Jennifer  <Best Regards, and I hope you will give live rock another chance! AdamC.> 

Substrate was Re: Ich question Anthony. The current CaribSea Puka is about 1/2" (barely covering bottom). <again... a labor intensive grade that is prone to trapping detritus...your call if you don't mind siphoning to keep it clean/sanitary> I've considered sand many times and could do it again. However from reading the FAQ's, is the DSB (about 3") good for a heavier bio-load FOWLR system ?  <yes in a properly managed system (adequate water flow, two skimmers, extra water changes, etc all appropriate for a heavy load tank> It contains eel, grouper, etc. As far as I know, eel and sand don't get along real well as they make a mess of it. . .  <some folks have complained about it... I have also had success with it including a 3' eel in a 500gallon display and several smaller species in smaller displays on fine deep sand. I am also very strict about not overstocking or overfeeding> I also opted not to since I didn't think I could keep any sifters alive in there (although you've mentioned one that could).  <there are many if you research/look into it to suit most any tank> Can a DSB keep up with heavier bio-loads or is it mostly more advantageous for reef based and light bioload systems ? <answered above> Water flow is heavy. 125 gallon is being pumped with 4 Maxi Jet's PH's (295gph), and return is Iwaki 70's (1500gph), so its about 10 times. Return is not broken up and fed from one side of the tank and forcing flow to the other end. That does bring up a good point, is it better to have powerheads down low pointing up or even to keep detritus up, or is better in the classic setup up high with the head pointing to whatever 'dead' areas you have in your tank ?  <any pattern that produces sufficient random turbulence to keep detritus in suspension is fine> If detritus suspension is the goal, wouldn't lower powerheads pushing current at the bottom be better ? <not necessarily if surface agitation is compromised to do so. Again...above recommendation for current> Again, can the DSB handle denitrification for higher bioload systems, or should a denitrator from Aquamedic (do these work) be considered. <no experience with the product> Obviously neither of the two will replace the small biweekly water changes. . . <exactly. Anthony> regards, Ed

Substrate was Re: Ich question III Hmm, yeah, I know the drawbacks with Puka shells. Been living with it for who knows how long. . . Guess it'll be time to switch one side of the tank and then the other. Here is a question though, is there any benefit to having a shallow sand bed (1/2" or so) ?  <simply aesthetic> The tank is only 18" tall, so I'm not sure I'm willing to allocate 4" to a DSB. . . <agreed> Yeah, my higher bio-load system, has a ton of filtration on it. I only have one skimmer, but its a dual-bucket system (two injectors) rated for 600 gallons. So I am over skimming a bit. . . < I certainly have no complaints with any skimmer that produces daily with consistency> Diverging to another question - can you have too many cleaner shrimp ? I have a few in the tank, but every once in awhile I lose one. So instead of constantly replacing one or two, can I drop like 6 or 8 of them in without any detrimental effect ? <sounds like a waste of precious life/resources until you figure out why they disappear or don't live for years. Anthony> Ed

Re: Substrate was Re: Ich question IV 1/2" of sand being aesthetic, but its more functional and better than 1/2" of Puka shells though, correct ? <agreed> I lose a shrimp to a lion every once in awhile. . . Not sure why the lion eats the shrimp that's cleaning it. . . One of those, biting the hand that feeds it in nature type of things. . . <wow... until these animals are captive raised, it seems like such a waste. I would not recommend adding any more. Anthony> Ed

Crushed Oyster Shell as Substrate? Dear Mr. Fenner, I have been maintaining a F/O 30 gal salt tank for about 2 yrs. NEVER a reef tank. I am trying to set up a 125 gal reef as inexpensively as possible without downgrading quality. So I am researching each and every purchase thoroughly before deciding. I am up to "substrate" at this point. <Okay> I am in the Midwest, thus sand/live sand is hard for me to get (without driving 150 miles) AND BOY! shipping for 200 lbs is crazy! My ONLY local fish store is "PETCO", big choices there! ;) I have also looked for the famous "Southdown" sand here and it's just not gonna happen without eBay prices and shipping. <Hmm, how about the Home Depot sand alternative? Please consult/consort (!) with our Chatforum (www.WetWebMedia.com is the homepage, link there... am on the road, can't cut/paste) re its availability in your area> I am also currently creating cement rocks with crushed oyster shell, something that I have PLENTY of in the Midwest ;). My question is, Could I possibly use the "crushed oyster shell" as a substrate?  <Hmm, well, can... please see the "Marine Substrates" section on our site (WWM) here> I have been searching forums and sites about this and have read about 50 "absolutely nots" and about 2 "I use nothing else". What do you think? <Possible, generally not advised... that is, typically, substrates are a plus> My uneducated theory is that if it's ok in the rocks, why wouldn't it be ok for the substrate? If you think it is possible, Could you recommend how deep? For a 30 gal hex & 125 gal? <Again, pls see the "complete answer" article on our site here> I'm sure you get a ton of letters, emails daily, and I thank you for your time and consideration! <have been out at the MACNA XIII hobby conference the last few days... sorry for the delay in response> Amy Horn P.S. I have ordered your "The Conscientious Marine Aquarist". I am patiently awaiting its arrival to my local book store. 1 week down, 1 week to go ! <You will not be disappointed my friend. A note of sorry in advance... for the hours we will share together in your reading of this work. Bob Fenner>

Substrate particle size Hi again, Well this is kinda off subject, but the sand I have in my tanks now is aragonite which is about 2-3mm in size. I have read in a variety of places its better to have sugar size sand (oolite?), so animals can burrow into it. I have also heard that there is a sand that hardware/home stores sell that can be used in the tank, which I'm sure is cheaper than buying it at the LFS. Have you heard of such a sand, and if so what is it called :). Thanks. Chris >> Hmm, I'd like to know what this sand is... at the hardware store... Most all I've ever seen are silicates (kiddie play box sand), metamorphic chondrites ("gravel" for freshwater), and maybe flints (good for some freshwater systems)... maybe dolomitious material or Tapashell (mainly calcium and magnesium carbonates) you could find at such outlets that were in "farming" areas... And, nah to the finer substrates (oolithic... fine, dusty stuff)... as being better... they have their own sets of problems. You're better off with the 2-3mm stuff of all about the same grade... Maybe place the sugar stuff in a refugium... Bob Fenner

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