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Changing Substrate

By Rob Layton, David Mohr and Rob Toonen. Posted to Reefkeepers emailing list, Saturday the 12th to Monday the 14th of February 2000.

Rob Layton

I'd really like to remove the crushed coral from my tank and replace it with sand. Does anyone have any suggestions on an easy way to do this? I figure there must be an easier way than scooping it out by hand. The tanks is a 37 gallon high tank. 1 yellow tang and a few rocks. I'd like to replace the crushed coral with sand and then start putting live rock in, I don't really like the look of the crushed coral. Thanks.

David Mohr

It's done all the time. -) Make up enough NSW to fill 1/2 to 3/4 of the the tank. First remove the tang and rock to a bucket filled with tank water and a powerhead and a heater. What I've done in the past is use the 16 ounce cups that you get soft drinks in, clean of course, and scoop it out that way. Leave about 1/2" of your crushed coral in the tank because this contains quite a bit of your denitrificating bacteria and critters. Your water is gonna get pretty cloudy and dirty so you can siphon off water until the tank is 1/2 to 3/4 empty. Now simply add your new sand on top of the crushed coral. Fill the tank up with the NSW you had mixed and wait for it to clear. When the tank is clear add the tang back.

Rob Layton

I was thinking of using one of the plastic containers my cat food comes in, it's 56 ounces in size, figured it would allow me to scoop the stuff out pretty easily. I was gonna put some holes in the bottom of it so I would just be taking out the crushed coral, is that a bad idea? Thanks for the advice.

David Mohr

IME going with a smaller scoop didn't stir up as much crud although it still stirs up enough. The idea is to remove the crushed coral yes, but to still leave 1/2 of the substrate fairly undisturbed.

Rob Toonen

Sorry, David, but I must say that I disagree with your recommendation to leave half of the substrate undisturbed. I know how tempting it is and that people worry about biological filter activity, but every time I've done this, I really regret it in the end. In the tanks where I left any of the crushed coral, I've usually decided to eventually take down the tank in order to get the stuff out of there, and I really recommend that Rob pull out all the crushed coral while he has the chance to do it easily now. The sediment sizes that you really want for a proper sandbed are much smaller than the crushed coral pieces, and boulders like that in a sandbed simply end up taking up space and requiring a deeper bed than you would otherwise need. If it were me, I would use a garbage can or some such thing and dump the sand into that with the "waste" water from a water change on an established tank.

Personally I do not rinse my sand at all -- one of the best sources of sand in the "clays and silts" size category discussed in the recent 2-part FAMA series (Jan/Feb) titled "Are Plenums Obsolete?" is the fines that most people rinse out of their new bag of sand. The best way to develop a good mixed sediment bed of fine sands, clays and silts is to just dump it all in a container and add some old tank water. If you're really interested in developing a good bacterial coating on your sand (which I'd recommend if you're replacing an existing bed), add a raw dinner shrimp tied in the toe of a nylon stocking to the mixture and let it age a little longer (it's easier to find and remove the nylon with the partially decomposed shrimp or squid bit at the end).

I then stir the sand well every day for a week or so (aim for 2 or so weeks if you want a decent bacterial load), and try to net out the sunflower seeds, bits of plastic and so on that float out of the sand so that those things are not added to the tank. After about a week or so, you simply dump as much of the waste water as possible, and add the sand to your new tank. By doing this you should safely have the chance for the sand to equilibrate (anything that is going to immediately go into or come out of solution will do so in that waste water), and for the sand grains to become coated with a bio-organic film. The two major advantages of this in terms of your sandbed fauna are that you will already have a good population of bacteria to support both your bioload upon adding detritivores, and a ready food supply (most of them eat bacteria off sand grains, and newly rinsed sand doesn't have much food for them). This means a much easier transition for the critters into your tank, so more of them survive, and that's a good thing when you spend a bunch of money to add a good starter culture of detritivores to your sandbed! In the end, this will also make concerns about disturbance of the biological filter capacity of the crushed coral irrelevant because the sand has a much greater surface area per unit volume, and the bacterial carrying capacity of your sand will far exceed that of a crushed coral bed.

As an added plus, it also makes it easier to add the sand to an aquarium because the particles will settle out of the water much more quickly, and you get less clouding of the water when you first add the stuff than if you simply dumped the entire load of sand directly from the bag...

In addition to the recent FAMA series I mentioned above, there is a lot more information about sandbeds, how they work and why archived at http// -- you might want to start with a quick read through that...

David Mohr

Don't be sorry Rob, any time to join our little discussions I believe we all learn a great deal.

According to one of your discussions on sand beds, which I participated in as I had my knuckles rapped a few times :-) you recommended 60% fine sands ( 0.5-0.05mm ) roughly 30 % silts and even some clays (0.001-0.05 mm) and 10 % course sediments of varying sizes from sands to boulders and substantial pieces of coral rubble. Would not that not include crush coral ? My question to you is what did you see in your tank that made you tear it down ? Are you disagreeing with the crushed coral being left in the tank or just not disturbing the 1/2" left in the tank ?

I would agree this is a better way to do it. I've never rinsed my sand either and every time I post that people think I'm nuts, not that that has ever deterred me. -)

Rob Toonen

Actually no, what I had in mind there was the live sand that you can buy from suppliers today. It all fits into this latter category, and at about 10% of the bed, any substantial amount of crushed coral left over generally leaves you with a lot more than 10% or so falling into that "big stuff" category. If you're not going to seed the bed with any live sand at all, then it probably wouldn't hurt to leave a little, but 10% of the volume isn't very much crushed coral.

My question to you is what did you see in your tank that made you tear it down ? Are you disagreeing with the crushed coral being left in the tank or just not disturbing the 1/2" left in the tank ?

I just couldn't get the sediment composition right, and over time the fine stuff settles down and the coarser stuff all ends up on top. If you're trying to keep tiger tails and the like that require fine sediments to feed successfully, that means that you eventually have to remove those chunks that cover the surface of the sand (a major disturbance which removes a lot of animals no matter how hard you try to avoid them), and if that happens frequently enough, you decide to rip the thing down and start again the right way (or at least I did)...

Created by liquid
Last modified 2006-11-24 18:41