flourite black sand

I guess I live under a rock.

Because it wasn’t until recently that I learned Seachem has a sand substrate called Flourite.

Since I love planted tanks, I knew right away I had to try this.

And frankly, the stuff is really impressive.

Keep reading to learn why!

What is Seachem Flourite Black Sand?


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Flourite sand is NOT soil.

Actually, it’s not really a regular sand either – because basically it’s clay ground to a sand-like consistency.

But unlike regular sand…

… This clay is able to provide nutrients to your plants.

(Without making a perpetually cloudy mess of your tank’s water like a fine-particle clay or dirt would.)

Another benefit is that the stuff doesn’t ever compact like dirt, which can make it difficult for some plants to root properly.

Flourite sand is a much smaller grain size than regular Flourite, which is more similar to gravel.

This is really good:

Particles of debris and waste do not settle down in between the crevasses like they would using regular Flourite or gravel, which makes cleaning more difficult.

The best part?

It never needs to be replaced because it doesn’t break down over time.

It’s like having 24/7 fertilizer for your plants.

Dosing with liquid fertilizers would just be the cherry on top rather than a required item for a beautiful planted tank.


My Review of Flourite Sand

I really feel that this black sand gives my tank a striking look, while still remaining natural.

Here it is in my Penn Plax rimless tank:

Some report that it looks a bit charcoal under certain lighting conditions.

To me it looks pretty dark.


For growing plants, it’s 100 times better than regular sand and can really help get you along a lot further in a beautiful planted tank – especially in a low-tech setup without added fertilizers.  I find plants root really well in this.

Couple that with the fact that cleaning is a breeze and this is a really awesome substrate.

I made the mistake of deciding to add more of it once I already was filling the tank with water.  Big mistake, because filling it up by pouring the water slowly over a plastic bag left the water pretty clear… until I dumped in more.

Then I couldn’t see past the front of the glass.

(Admittedly I did not wash it first – my first mistake!) 😛

After a large water change, I was able to see through the water well enough to start planting, but my takeaway is do not add water until you are 100% done adding the sand or it will be a huge mess.

Some people have issues with residual cloudiness in the first week of setup, which can be due to disturbing it like I did.

This does go away on it’s own…

… But I have a secret for you that I use for this problem:

Run a sponge filter and wring it out every 8 hours and your tank will be crystal clear in a few days or less!

Or wash it well first (if you don’t want to have to do that.)

Now here’s something else I’ve found:

The tank I use Seachem Flourite Black Sand has been having consistently 0 nitrates.

You heard that right…

And it’s stocked higher than my other tanks!

I contacted Seachem about the possibility of good anaerobic bacterial activity occurring in this substrate which could be reducing my nitrates, and they confirmed that this is likely the case.

See, clay has 10,000x the surface area of sand.

So it supports WAY MORE bacterial activity.

Another benefit?

The trace minerals in this clay continually supply the water column with essential trace elements for my plants and fish.

Not having to do water changes more than makes the price worth it (though I can’t guarantee it will happen to you as every setup is different).

But for what it’s worth I used 1 bag per 10 gallons, which gave me about about a 1.5″ layer of sand (the substrate is sloped from front to back in my tank from about 1″ to higher in the back).

In my opinion?

Five stars.

How Much Flourite Should You Use in Your Tank?

For the planted aquarium, you really should have at least 2″ of this stuff at the bottom of your tank.

More if you have a lot of deep rooting background plants.

A good rule of thumb is 3.5-2 kg per 5 gallons of water for 1.5-2″ deep substrate.

You can also do more.

Deeper sand beds can also provide space for good anaerobic bacteria to grow that remove nitrate, helping to create a stabilized ecosystem.

Good news:

Plant roots help prevent hydrogen sulfide pockets forming in the sand.

(The good news is stinky and toxic hydrogen sulfide is often a major problem in dirted tanks.)

Quick tip:

Love Seachem Flourite black aquarium sand, but aren’t sure about the black?

Flourite sand also comes in brown.

Maybe you want a lighter tan or other color of substrate?

One thing (I want to try this to know for sure and will update if it works out okay) to try is putting wet bentonite clay or sand around the edges of the bottom of the tank BEFORE adding the Flourite sand in the middle. Then you could top it with the bentonite/other color sand before planting.

This would not work for fish that like to dig.

Here’s something interesting:

The following interview was recovered from from https://web.archive.org/web/20101205053208/http://www.aquabotanic.com/flourite.htm:

An Interview with Seachem on Flourite

By Robert Paul H.

What exactly is Flourite made of? What type of clay?

All I can say is that it is a naturally mined clay (i.e. it is not “manufactured”).

What is the significance of “fracted”?

Basically a fancy way of saying the clay has been shattered or broken into many small pieces of suitable size for a planted tank.

Does it provide a source of Fe? In what form?

Yes. Ferric mainly.

Does it need a chelator?

No, the plants roots are able to extract all the iron they need directly from the Flourite (just as they would extract from the soil out in the “real” world).

Does it provide any other trace elements?

I’m sure there are some, but we haven’t had it analyzed for the main reason being that the report would not tell us if said element was in a useable form or not, thus we wouldn’t want to supply misleading information (i.e. source of X, when in fact the plant get at the X even though it is there). We know it can extract the iron based on a simple qualitative test e.g. plants simply do incredibly well when planted in Flourite. I know that sounds like hype, but in this case it is just simply true… plants that were doing so-so or dying, when switched to Flourite simply take off. Anyway… the proof is in the pudding . You’ll just have to try it for yourself to become a “true believer”.

What benefits does it have over laterite?

  1. Will not crumble and fall apart leaving a muddy mess in your tank
  2. Completely obviates the need for laterite as it does what laterite does (provides iron) and what a good gravel does (a place for roots to grow and looks really nice).

How long does its available iron last? Should it be replaced after a given period of time? Is it considered inert?

The iron should last for years. It’s been on the market for about a year and half now and we have tanks that have never had their Flourite replaced and they are still doing great. It is considered inert, i.e. none of it will dissolve into the water column… it is for the roots only.

In general, what benefits, or what makes this product attractive to the beginner?

The main benefit is the simplicity of it. You can use just Flourite as your gravel and really don’t “need” to use any other iron supplements. Flourite will provide a good solid base of good growth. Supplements will only enhance on top of what Flourite already provides; the choice to add them is optional depending on personal taste and preference. Flourite also provides somewhat of a safety net, i.e. if the hobbyist forgets to add their iron supplement for a few days (or goes on vacation), the Flourite will carry the plants on through and keep them from dying (which could have happened if Flourite were not in use and all supplements were suspended).

Gregory Morin, Ph.D., Research Director, Seachem Laboratories, Inc. http://www.seachem.com 888-SEACHEM


This sand is probably one of the best substrates money can buy.

If you want a beautiful planted tank with the least amount of effort, Flourite black sand is a must!

So what do you think?

Have you tried it before on any of your tanks?

Let me know your thoughts in the comments below.