Beginner Topic Reef2Reef FAQ #1: Substrates

A beginner FAQ on substrates complete with the most common questions that we get in the forum.
  1. A reef aquarium with a black sand substrate.
    Photo is from the Reef2Reef archives, 2018.

    It’s time for some FAQ’s. I’ve said before, but it bears repeating, there are often many different ways to do things when you have a saltwater aquarium. This document will by no means be an exhaustive treatment of any one subject. I’ll offer answers that are short and sweet, quick and dirty. I will, however, give you links to where you can read more on the subject, and I will include those references at the end.

    There are lots of questions that we get in the forums over and over again. Which is fine. Please, if you’re a beginner, feel free to ask questions. There are no stupid questions. But we thought that some FAQ’s might be helpful to beginners.

    Wy Renegade from the forum has written a very in-depth article about substrates which is a sticky in the beginner forum. Below are some briefer answers to common questions that revolve around the same subject. So, here we go.


    What's a substrate?

    The substrate is what covers the bottom of the aquarium.

    What kind of substrate should I have?

    There are basically three (3) types of substrates for a reef aquarium: bare bottom, a shallow sand bed (SSB) or a deep sand bed (DSB).

    What you use depends on you. It depends on your taste, your goals, and your livestock. Different livestock have different needs and requirements. So, I’ll go over them briefly.

    Bare bottom is easy to clean, and it gives you a clean, sterile, and contemporary look. It’s what we usually recommend for quarantine tanks and hospital tanks and grow-out tanks if you’re breeding. It’s not appropriate, however, for some types of livestock.

    If you want, for example, a shrimp/goby pair, then they need something to dig in. This is why it’s important to have some idea what you want in your tank before you start to set it up. It’s possible to change and add sand at a later date—after your tank is up and running—but that’s not the easiest or best way to do it.

    A shallow sand bed (SSB) is sand and/or a mixture of crushed coral or other that’s typically zero (0) to < two (2) inches deep. It looks more like a natural setting, but that shallow bed will collect junk and need to be vacuumed (siphoned) regularly. The depth of two (2) inches to four (4) inches is not recommended. It’s too deep to keep it clean but not deep enough to aid in chemical filtration.

    A deep sand bed (DSB) is a minimum of four (4) inches deep to six (6) inches or more. A DSB when set up correctly with the right type and size of sand grains will eventually help with filtration because anaerobic bacteria colonize the bottom and help to absorb unwanted nutrients converting them to nitrogen gas.

    Some people think a DSB is unsightly and they set up a remote DSB or RDSB. That means putting the DSB somewhere other than your display tank, like in a sump or refugium which is connected to the main tank. This allows you to benefit from the chemical filtration without having to look at it constantly.

    What kind of sand do I use for my substrate?

    That depends. There’s not a one-size-fits-all answer. If you want a DSB, then you need a very small grain size. You can use calcium carbonate sand, silica sand, aragonite sand, oolitic sand, quartz sand (like pool filter sand), pulverized limestone, or sand blasting sand if it’s inert. You want to avoid any sand that has additives and/or unknown metals that can leach into the water. For a DSB, some people have experimented with something called Miracle Mud, a silty substrate often used in a planted freshwater aquarium. What’s important is having a smooth grain, which won’t hurt your little critters digging in the sand.

    For a SSB, you are not limited to fine grain size.

    The color of your substrate will affect the amount of light that is reflected in the aquarium for better or for worse.

    Can I use something other than sand?

    You can use something larger-grained like calcium carbonate gravel or dolomite gravel, but it’s often hard to keep clean. You couldn’t use this for a DSB, but you could for a SSB. In fact, for a SSB, you can use whatever you want if it’s inert. You could even use glass beads (if it’s not float glass) if that appeals to you. But most reef aquarists try to achieve a natural look.

    What’s important is that your substrate A) is appropriate for the livestock and B) will not potentially hurt the water column. There are no aquarium police who will come to your house in the middle of the night to examine your substrate.

    It used to be thought that using a calcium-based substrate was preferable because over time it would dissolve (a little) and help keep your pH up. There’s newer research now showing that’s not exactly true. Calcium sand doesn’t dissolve unless the pH is much lower than in your water column, so, you can’t count on your sand to “buffer” up the overall pH and add calcium to the system, and inert substrates perform well. That said, if you have critters that are used to digging in sand, then you need to give them sand to dig in.

    Jawfishes in a large-grain substrate. Jawfishes are from the family, Opistognathidae.
    Photo is from the Reef2Reef archives, 2018.

    Can I use the colored gravel I had in my freshwater tank?

    No. You have no idea what chemicals were used to make the gravel different colors. There’s too much danger of bad things leaching into the water column. Unless you want to get it professionally tested by a lab and also get an opinion from a chemist about whether it would dissolve in your saltwater or is inert.

    Do I have to rinse the sand before using it?

    You don’t have to, but most people like to rinse it because you’ll help to avoid a big cloud in the aquarium if you rinse it first. People typically rinse it with tap water then use RO/DI (reverse osmosis/deionization water in the final rinse.

    Can I move my old sand from my old tank to my new tank?

    Sure. Why not? But if the tank is several years old and mature, then you have to rinse your sand first. If the tank is young and under six (6) months old, then you don’t have to rinse it.

    Can I add sand when my tank is already set up and filled with water?

    Yeah. Sure, but it may be cloudy for a while. Eventually the sand will all settle.

    What is live sand?

    Live sand is sand that has a bunch of microorganisms in it which are beneficial for your aquarium.

    Do I have to use live sand?

    No. If you have live rock, some of those organisms on it will probably eventually colonize the sand. You could also get a little live sand from a fellow reef aquarist with an established tank, assuming you’re confident that there’s nothing harmful in this sand. If you add a little live sand, eventually the organisms in that will spread throughout your sand.

    Live sand is good for the aquarium, but you don't have to use it.

    NB: Please note that using black sand is not mainstream, and with some black sands, there are dangers of nickel, vanadium, and other metals leaching into the water column.

    A Remote Deep Sand Bed (RDSB) in a refugium.
    Photo is from the Reef2Reef archives, 2018.

    A special thanks is due today to the following individuals:

    Forum member hdsoftail1065, who is always available to discuss articles.


    Reef Aquarium Substrates:‘tan’.461811/;jsessionid=19hy31e505qnr?sequence=1


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    Author Profile: Cynthia White

    Cynthia received her BA in English from NYU during the Paleozoic Era. She has been a freelance writer and editor for over 20 years. She has written for newspapers and magazines, both in print and online and was formerly a marketing manager for a small oil company. Now she is a writer and editor on staff at R2R, where her forum nickname is Seawitch.

    For 15 years, she kept a dozen freshwater tanks, bred cichlids--Cyphotilapia frontosa--and sold them to pet stores in Calgary. Finally, after years of study, she has come to saltwater side. She lives in British Columbia, Canada, with her husband and three special-needs dogs, a five-minute walk from the Georgia Strait.

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