The Truth about Sand in a Saltwater Aquarium

Think you know all about sand for your saltwater aquarium? I thought I did, until I learned the truth about sand by listening to the ReefThreads podcast.

aquarium sand by gurdonark
Saltwater aquarium image by gurdonark

In their podcast 124, Gary and Christine (the usual hosts, if you don’t listen to the podcast) had a guest on named Boomer, who sounded like he knew everything about sand you could ever want to know…and quite frankly, he confirmed that a lot of what I thought I knew about sand was wrong. So unless you have a bare bottom reef, you’ll love this podcast. I highly recommend you download and listen to it, today.

So, if I ever gave you bad advice about sand, I apologize.

Before listening to the podcast, I had 2 pretty firm beliefs about the use of sand in a saltwater aquarium:

  • Belief # 1: Aragonite sand in a saltwater aquarium can have a beneficial effect as a buffer and calcium source.
  • Belief # 2: Sand containing silicate could be disastrous in a saltwater aquarium because it will fuel the growth of problem algae.

Well, it turns out that both of those beliefs (which I believe to be broadly held by a lot of aquarists) are wrong.

crushed coral
Note the crushed coral in this image by smoMashup_

It turns out that aragonite sand initially DE-BUFFERS saltwater—and once it stabilizes in your saltwater aquarium, it isn’t going to do much of anything at all unless your pH drops crazy low—as in below the pH of neutral freshwater. So…eh…I humbly apologize for not know that. It kind of blows my mind. I’m positive I’ve read the OPPOSITE of that in a bunch of places. The buffering capacity of the sand is often touted as a benefit for keeping the pH of your coral aquarium stable.

As far as silica-containing sand…Boomer said that the glass that your aquarium is made from is going to dissolve faster than the silica (he also called it quartz) in the sand…so essentially, that whole thing about fueling problem algae (diatoms, cyano, or algae) is bogus.

From my perspective, there are 2 morals to the story:

  1. Buy whatever sand you want. Go for aesthetics—not chemistry—the sand appears to be roughly inert (at least to the extent we’re interested).
  2. Don’t believe everything you hear or read…even from guys like me. There is a lot of good information out there, and there is a lot of bad information out there. I try my best to put the good out there—but do your homework—and let me know if you find something on the site that may need some adjusting—my goal is to be a helpful source of information.

So what do you think about that? Are you as surprised as I was to have these myths debunked?





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