# Adding Onyx on medium gravel



## amber2461 (Sep 26, 2004)

Hi

I have an existing 20 long gallon with medium sized gravels.

I just recently purchased 1 bag of Onyx sand. I was wondering if I removed the fishes (7 pristellas, 3 ottos, 1 SAE), remove 50% water

a) Would it be safe to pour in the onyx sand?
b) Would the tank cycle again?
c) Is it advisable to do so?

I just need confirmation before I start anything and might regret doing it later.

Thanks


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## Rex Grigg (Dec 10, 2002)

You are going to need to rinse the Onyx sand. If you don't your tank will become a gray mess. And it will stay that way for a very long time.


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## jhoetzl (Feb 7, 2005)

You also have to be a little careful of capping the existing gravel. I wouldn't just pour it over the top as some nasty bacteria might get trapped under the sand layer, and, depending on the size of the existing gravel, the time it takes to settle down to the botton isn't usually quick enough to avoid that problem.
So you will probably have to mix it in with the existing gravel, which will cause a bit of unstability in the cycle.


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## scolley (Apr 4, 2004)

amber2461 - I put an inch or so of Onyx over my flourite, thinking that a nice "black" bed of sand would look nice over the larger grained flourite (kinda like your gravel).

Well, if I'd done a bit of searching here first I would have found out two things that were both disappointing:

1) That "black" Onyx looks gray in the tank. Not black.

2) And worse, after any reasonable amount of planting/replanting, that Onyx just mixes in with the stuff underneath it. And eventually the largest grained stuff works its way to the top. So from the top looking down, that Onyx is gone. Bye bye Onyx. :icon_sad:

Think a about a bag of popcorn at the movies. When the big pieces are mixed in with the little pieces as you get toward the bottom of the bag. So what do you do? Give the bag a good shake, and all the big pieces come right up to the top! If you dig in that substrate, you'll be doing the same thing.


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## amber2461 (Sep 26, 2004)

Hmmmm ... I see ... ~sigh~ Thanks for the speedy replies though, appreciate them!


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## amber2461 (Sep 26, 2004)

If I removed all the fishes into a bucket and keep 50% of the existing water, I could remove the existing gravel and then remove some of the remaining water.

If I were to rinse the Onyx sand thoroughly, put them back in to the tank, slowly add in the 50% of remaining water and then let the water clear (2-12 hours) would it be okay then? I would still be using the same filter of course.

Wait 12 hours before putting back the fishes and top up the water, is it advisable to do this then?


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## scolley (Apr 4, 2004)

Marge - you are suggesting a method of putting the Onyx in the tank, which sounds reasonable enough. But it raises a possibly more important question...

Is Onyx alone sufficient as a substrate?

I believe Onyx sand is nearly inert, or at least nutrient free, as opposed to soil, Eco-complete, Flourite, and a few others. And there are some that will tell you that you can keep plants by fertilizing the water column only, with no nutrients in the substrate. Others will say you can overcome an inert substrate with supplements like root tabs (not Jobe spikes though!).

But I don't think you'll find anyone that will tell you that your plants won't grow _better_ in a substrate with some nutrients in it.

IMO, I'd get a bag of Flourite (maybe 2) and mix it in with that Onyx. But don't take my word for it, use the Search function on the word _Onyx_. Or wait for some other opinions. :smile:


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## Bichirdude (Apr 16, 2005)

I've got Onyx in my ten and it works perfectly fin by itself. I think there has to be some sort of nutrients in there. That being said, when I upgrade my tank I'm going to go with an Onyx flourite mix. I'll probably try to layer it as well and just expect it to shift over time. 

Scolly, My black onyx sand still looks perfectly black, maby you got a bad batch, or maby somebody pulled the 'ol switcharoo on ya. I've never heard of it looking grey in the tank before.

I can only imaginec that you're planning to do a planted tank. how deep do you plan on having your substrate? When I first set up my tank, I got a little greedy for space and only ended up with about an inch of substrate in the tank. Just a firendly reminder not to make thte same mistake I did.


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## scolley (Apr 4, 2004)

Bichirdude said:


> Scolly, My black onyx sand still looks perfectly black, maby you got a bad batch, or maby somebody pulled the 'ol switcharoo on ya. I've never heard of it looking grey in the tank before.


I certainly might have. But I _have _ heard other people complain about this, on this forum even. I know a search on Onyx will pull up a lot of hits, maybe too many to peel through. But should you care to try, you will definitely find that I'm not alone on this. In fact, till you posted this, I assumed it was always gray for everyone.

Sounds like a quality control issue to me. Should there be any doubt's you can go to this thread, and see for yourself. Unless maybe what I call gray, you are calling black?


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## Bichirdude (Apr 16, 2005)

well, my vision isn't quite what it used to be. It does match the black trim of the tank however. It never occured to me that Onyx sand would turn out grey. 
Is it a dark grey or a light grey? 
Was it black in the bag and turn grey in the tank? 
Did you buy it at a petsmart or a smaller operation?

Incidentally, I'm going to pick up some more Onyx sand today and I'm setting up a new tank tomorrow. I'll try to post on how it goes. I think a really dark grey would be pretty nice in the tank I'm invisioning.


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## scolley (Apr 4, 2004)

Bichirdude said:


> Is it a dark grey or a light grey?


I'd call it neither dark nor light, but medium. Look at this post  and see for yourself.



Bichirdude said:


> Was it black in the bag and turn grey in the tank?


In the bag is was quite black. But when poured in the water, with the lights on, it looked gray. I suspect that the color didn't actually change, but that the light reflecting off the surface of the grains just made it appear gray.



Bichirdude said:


> Did you buy it at a petsmart or a smaller operation?


Got it from a web retailer, don't remeber which one. Good chance it was Big Al's.


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## Anthony (Jan 11, 2005)

I mixed onyx with eco-complete and I love the color. The only complaint I have as has been stated is the large "rocks" in there. I still haven't taken the time to remove them all. Also Drs. Foster&Smith's site said it will aid in buffering the water.


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## aquaverde (Apr 15, 2003)

*Comparison photo*

Top row: Eco-complete, Onyx sand, Volcanit, Flourite
Bottom row: Tahitian moon sand, basai soil

Just happened to have a variety at the time, so thought to snap a pic.


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## scolley (Apr 4, 2004)

That's quite the assortment to just have laying around James!

I know that I have a bit of trouble with my color vision, but that Onyx looks pretty gray to me, and it's not even in a tank.


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## Bichirdude (Apr 16, 2005)

when I ordered my onyx sand this last time the guy asked me what color I wanted. until that moment it hadn't occured to me that it came in any color other than black.


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## bharada (Mar 5, 2004)

The Onyx sand I saw in a friend's tank was pretty much the color in the James' post. 

When I was growing up in Hawaii the LFSs used to sell black volcanic sand. Very black and shiny, and totally inert with grains about 4x the size of Tahitian Moon Sand.


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## aquaverde (Apr 15, 2003)

My pic was taken last year when I was toodling around setting up my 65. I was experimenting around with a number of different substrates, and had a little in each bag left for such a time as a comparision photo could be done. I dumped the whole mess in what is now my shrimp tank. I've purchased Onyx several different times. I like the grain size way better than Flourite, but it buffers the water and I'm not sure I always want that happening. It's definitely been the same color every time I got it, but there was a point when the grain size became more uniform. I think the processing might have been tweaked a little by Seachem at that point.

The only really black substrates I know of are Black beauty (some sort of coal product used for sand blasting), Eco-complete (and it's not jet black) and Tahitian Moon Sand. I have eco and TMS sectioned off in my 65.


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## Bichirdude (Apr 16, 2005)

I suppose it's possible I got duped. I may have tahitian moon sand. how does it match up to flourite and Onyx?


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