# Onyx (Grey Coast Calcite)



## niko (Jan 28, 2004)

A week after setting up my new tank the 100% RO water in it has a KH = 6 and GH = 6, with pH of 8.0 (no CO2 yet). I attribute these high numbers to the layer of Onyx that tops a peat/pumice/laterite mix.

I read all threads that concern Onyx and aside from Tom's multiple assurances that it works I couldn't find any detailed information.

This thread contains an e-mail or a letter from Seachem that doesn't explain much either. From Tom's post in that thread one can easily conclude that Onyx will become a "wonderful" source of Ca in a CO2 enriched water, providing ever growing KH and GH plus high pH - not what I'd like to have.

So how does Onyx behave in a CO2 enriched water? Does it endlessly produce Ca (and high KH, GH, pH)?

--Nikolay


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## Rex Grigg (Jan 22, 2004)

Onyx is going to buffer the water. Pure and simple I can't tell you when it's going to stop. I have had some in a tank for almost two years and it's still working. And that's without CO2 injection.


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## plantbrain (Jan 23, 2004)

N-
If you use RO water, anything with Ca and CO3 is going to increase, Onyx does not seem to cuase a raise in KH/Gh after a few weeks when you use tap water with a KH/GH of 3 or so.

I change the water around 50-70% weekly, there is liitle issue with onyx in this case.

Why are using RO in the first place?
If you insist on RO for the fish, use flourite, not onyx.

Onyx is good since it adds some GH/KH to soft tap waters, it has little significant effects on hard water.

If you have an issue with higher KH/GH,s try some water changes.

I see no issue with higher KH/GH's as far as the plants are concerned, even if the KH rises, the CO2 rate will be essentially the same so your plants will be fine.

The only potential issue here is fish and most are fine with gradual raises and declines.

What fish are you keeping?

Regards, 
Tom Barr


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## niko (Jan 28, 2004)

Rex,

How often and how big are your water changes? I assume it's tap water, is that correct? 
As I mentioned I'm not too happy with parameters that I consider messed up so I was hoping for a few week period of heavy water changes to resolve the problem...

Tom,

I feel uneasy being unable to use the CO2 chart as a result of using a substrate that affects the KH/GH. I do agree though that even if the KH or pH are high the plants can grow with no problems. The big tank at the LFS that I set up few months ago had these very issues because of the Eco-Complete, but the plants did great.

I decided to use RO in my new tank because I recently had a great experience with another tank that is 90% RO.

It's interesting that tap water over Onyx would not cause a significant raise of the KH/GH, I didn't know that. Is that the same with Eco-Complete?

I don't have fish in the tank yet.

--Nikolay


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## Rex Grigg (Jan 22, 2004)

I do 25% water changes in that tank every week. And I do the changes with tap water. But the tap water here is very soft. Normally out of the tap it has no detectable hardness.

And you can still use the CO2 chart as it's adding carbonate based buffers to the water.


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## plantbrain (Jan 23, 2004)

Nothing to be uneasy about with CO2, test the KH , test the pH... done.

Success with RO is not from the RO, it's some other factor.
CO2, lighting, nutrients.

Unless the tap has less than the RO, your issue is noit from the RO water.

Why take something out and then add it back again?
Got nothing better to do? 
Seems awful silly and there's no merit to RO helping plants in any way except in a few very high Cu/Ns well water systems which are very rare and are private well systems.

Anyway, the Onyx is adding the KH/GH back for you.
When you have larger diff in concentration, there will be more dissolution.
So softer water will dissolve more than harder water.

Regards, 
Tom Barr


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## cS (Jan 27, 2004)

I find it amusing to have these kinds of threads, and those where people advise using muriatic acid to make sure that no Ca/MgCO3-based rocks are used in the aquarium for fear of raising GH/KH. :biggrin:

Reminds me of threads where hobbyists beg for snails to add to their tanks. And then there are threads where hobbyists clamor for methods of eradicating all snails. :mrgreen:


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## pineapple (May 4, 2004)

Surely, "Grey Coast Calcite" says it all. What type of calcite is not calcium carbonate?

Adding it atop a carefully thought out layer of peat/pumice/laterite seems odd to me. I would have thought Flora Base or something would have been more appropriate.

But as cS says, it is indeed humerous to see these arguments dither from one side to the other.

Andrew Cribb


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## plantbrain (Jan 23, 2004)

niko said:


> Tom,
> 
> I feel uneasy being unable to use the CO2 chart as a result of using a substrate that affects the KH/GH. I do agree though that even if the KH or pH are high the plants can grow with no problems. The big tank at the LFS that I set up few months ago had these very issues because of the Eco-Complete, but the plants did great.
> 
> ...


No fish? Then it will not matter. The tank will stabilize soon anyway as far as pH/Ca/KH etc.

All submersed substrates over time tend to neutral pH's.
Bacteria and redox causes this to occur.
The peat in the beginning offsets the KH/GH rises.

I added peat to 4" on onyx and it had the same KH of 3*(fairly low) as the tap water.

This went on for 20 months till I left FL. I also do large 50-70-% weekly water changes. That will even things out also.

Like I said, you can measure the CO2 easily.
The rate of CO2 is still the same being added even if the KH rises.

So the rise in KH only matters if you use a pH controller, both the pH/KH might change, but the CO2 content will be the same as will be bthe uptake of CO2 by the plants. There is a little error in this, but the genal notion here is fairly robust.

Using hyper soft water will cause the onyx to or CaCO3 etc to release more than harder tap water also.

Regards, 
Tom Barr


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## Simpte 27 (Jul 16, 2004)

I have fish in a planted tank and my water changes are exclusively R.O. water as my tap is liquid rock. (GH in the 30's-40's and KH in the 30's. PH anywhere from 7.8 to 9) Why is using R.O. bad?


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## plantbrain (Jan 23, 2004)

RO is bad if you want to do lots of water changes and don't have a reservior, or you have large tanks etc and don't mind the hassle and expense of producing RO.

Where do you live that has a KH of 30+?
That's 3x seawater and the GH would suggest a Ca levels of close to 1000ppm.

Pretty unlikley, maybe not impossible but pretty close.
KH's of 20 and GH's of 20-25 are typically the max amounts even in deep limestone waters.

Regards, 
Tom Barr


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## aquaverde (Feb 9, 2004)

I tested the water this week in my non-CO2 tank that has Onyx sand mixed with some Flourite and gravel. My water is very soft, KH 1 and GH never higher than 2, usually less.

I measured KH 5 and GH 9. The tank has been set up for 15 months. I add no fert or chems to the water.


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## plantbrain (Jan 23, 2004)

That's about what my non CO2 settle in at, I did no water changes for several months.
Plants need Ca/Mg and onyx allows me not to dose them in a non CO2 tank(less work).

Regards, 
Tom Barr


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## aquaverde (Feb 9, 2004)

This convinced me not to use Onyx in my high light tank so that I could have water hardness flexibility. In high light, you are having to dose regularly anyway, so not much is saved maintenance-wise through the use of Onyx.


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## Simpte 27 (Jul 16, 2004)

I live in Miamisburg ohio. My water is so bad, If I pour a glass of tap water, let it sit for a cpl of hours I can see sediment in the bottom of the glass. May be worth taking a pic of.


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## plantbrain (Jan 23, 2004)

Seems that folks with softer waters would like not having to worry about KH/GH getting to low.

SF folks like it for that reason(KH/GH's are very low, like RO).

You folks are doing water changes aren't you?
That evens things out.

Also, calcite can be very tough to dissolve in harder waters etc. It's not nearly as easy as aragonite.

I've used both flourite and onyx for years now.
Never had any issues with CO2, plants or any sort.

Regards, 
Tom Barr


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