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Discussion Starter · #1 ·
I saw "Onyx Sand: Gray Coast Calcite" on sale at Petco for $6.29 per 22lb bag. I have heard several people mentioning the same about their Petco's from other cities, so this might be some nationwide phasing out of merchandise.

I am not a fan of Onyx but there are lots of folks who swear by it; so take advantage of the special pricing. Onyx Sand, sold under the planted tank section, is the same as the gray coast calcite, sold under the marine section.

Good luck.
 

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Pnyx is good for plants. Has Iron is porous the buffering capacity is .1-.5 KH. That is NOTHING. Why worry about it DANG. i am going to use it on my next 60 gallon. It is better than Eco-Complete IMO.
 

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litesky said:
Does Onyx sand benefit plants in any way? What about PH buffer?
I was doing some research on Onyx a while back when I was considering substrate choices and here are what I can recall:

Onyx contains Fe as well as reactive Ca/MgCO3. As a result, it raises GH/KH depending on your tap water: soft water is affected more and likewise, hard water less so. The addition of CO2 will cause the sand to increase GH/KH even further. Is there a cap? Perhaps, I honestly have no idea. I have however come across several references where hobbyists using CO2 noted a range of 3-5 degrees increase. Your mileage may vary of course. If so, then please do share.

Onyx is sand. Sand is not very porous and thus has poor CEC. Not a big deal since most of us rely on water column fertilization.

Another concern with using sand is "compaction" that can harbor anaerobic bacteria who produce toxic compounds that are harmful to both flora and fauna. Compaction is more likely to occur in larger tanks where the resulting pressure from the relatively larger volume of water plays more of a role. But if you have medium to small tanks, then compaction is less likely of a problem.

Onyx sand contains A LOT of dust that you DO NOT want to wash all off because you will probably lose half the bag. This dust is a big issue for me. Scavenging shrimps and bottom dwellers will constantly disturb the substrate and these particles will be released into the water column and cloud your water. This is particularly annoying for me. But if the water current in your tank isn't strong, then this cloudiness issue is less of a concern. Over time, the smaller grains will settle to the lower layers of the substrate so the cloudiness issue will also be less frequent.

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Thomas Barr likes this stuff a lot, if you are swayed by that sort of thing. :biggrin: As far as commercial substrate choices in the USA are concerned, here are the four big kahunas: Eco-Complete, Flourite, Profile/Schultz Aquatic Plant Soil, and Onyx/Gray Coast Calcite. They all have their pros and cons.

I think that should cover it all.
 

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You can see all the other post I've made over the years about it.
It's not just my fav, several others will say the same.

Also, never knock it till you try it. I rinse 3x, add, never had an issue, never lost a bunch of it.

My KH/GH is similar because I add peat. After the effect from the peat wear off, the tank stabilized and so does the KH/GH through bacterial action.

I do large water changes anyway so this doesn't influence the KH/Gh much. A small rise during the week does not cause any issues near as I could ever tell.

Aesthetics has a fair amount to do with things, but I seldom have open gravel in my tanks, so the color does not matter a great deal.

Ability to get the plant in and out with ease is the prime thing for me along with plant health.

If you want soft water fish etc, then Flourite fits the bill.
Regards,
Tom Barr
 

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Dang it, where are all y'all from?! I've never seen Petcos here carry Onyx. Maybe Fluorite, and that has always been arond $25 a bag. Still, I went searching in 3 different locations in Houston and didn't see anything remotely resembling Onyx. You guys are truly lucky!

Paul
 
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