Aragonite sand as a buffer or myth?

[apophis924]

Randy i have had a GOOD size sand bed of sugar sized aragonite for some time and have not notice any buffering ablities as so many claim. If this is the same type of matrail used in ca++ reactors and a ca reactor uses CO2 to lower the ph so ca and minerals will dissolve and this effluent from the reactors usually has a low ph. How can my sandbed of aragonite be a buffer. wouldn't my Ph have to drop as low as a ca++ reactor to release the ca and buffering compounds? As far as the so called "slow disoution of aragonite" I can replace my trace minerals faster with a water change. From the readings i have done the ph has to drop to near 6 or 5 before the aragonite begins to realse any significant ca and or buffers.
Please explain the ONLY reason i was running the DSB was for the so called buffering abilites that i have yet to see.

[Randy Holmes-Farley]

The only way that an aragonite sand bed dissolves and does anything to the water chemistry is when the pH drops down inside of the sand bed (which it does due to degradation of trapped organics). IMO, this effect is small in nearly all aquaria, and is not a particularly useful or important way to add calcium, alkalinity, or to "buffer" pH.

please explain the ONLY reason i was running the DSB was for the so called buffering abilites that i have yet to see.

Sorry, you will likely be disappointed. Most folks use DSB's to reduce nitrate, not to add calcium or alkalinity. They can be effective at reducing nitrate.

[apophis924]

Thanks man at last a direct honest answer. Nothing like the purity and truth of chemoistry and mathematics.
Better reefing thru sound chemistry.

[Randy Holmes-Farley]

Better reefing thru sound chemistry

Hey, that's a nice motto!

[apophis924]

Its not copyrighted and you are more than welcomed to use it your post and or profile. If ANY has the right to use it is most definetly you Randy!

[Randy Holmes-Farley]

Thanks.

[Elric]

What about a black sand....this effect my be small with Aragonite and not have much of an effect. But does a similar effect with negative results come from using a black sand?

[Randy Holmes-Farley]

Black sands aren't calcium carbonate, and so won't buffer the water, although they may release harmful chemicals. I'd only use natural black sands that had been washed for a long time on a beach.

[Boomer]

Randy I have had a GOOD size sand bed of sugar sized aragonite for some time and have not notice any buffering abilities as so many claim.

This is true to a point, as far as the gravel buffering the water and has really nothing to do with the aragonite dissolving. It deals with an area of chemistry that involves solution kinetics at the water surface grain interface. It has been studied quite a bit and even test done by AS on the ability of certain calcium carbonate gravels to maintain a pH for a longer vs other carbonate gravels were a silica sand is used as control. I belive Randy brings it out in one of his articles. Certain gravels have a greater affinity for growing Hi-Mg-Calcite on their surface. Hi-Mg-calcites are the most soluble of the calcium carbonates. It is these surface "poisons/overgrowths" that end up going back into solution and buffering the water. However, they are very short lived. In time, days, bacteria will coat the surface grains and even these growths will not go into solution, as the are not exposed, unless the pH falls to a much lower level. As you probably have figure out by now it is pulling some of the waters carbonates and Ca out of the water. So, it is not the gravel but it is because of the gravel being a carbonate and no such thing exists with a silica sand. There is a review of this in Spotte.

What about a black sand

Almost al black sand is Basalt and igneous rock lava. As far as buffer goes it would be about the same a silica sand but as Randy pointed out there is the problem of leaching. The smoother the grain the better off you are.