travertine stone under bio-balls?

[mappa]

Anyone have an opinion on this? I want to fill my lower sump with broken travertine, under my bio-balls. It would make sense as it is porous, but not sure on its buffering capabilities in a +/- way. Considering that travertine is usually calcite or arragonite, and both are used in salt water fish tanks for buffering...it makes more sense to me. I would also be using lighter colored material that likely has less impurities than darker travertine.

[Ninong]

Keep this in mind, the claimed buffering capacity of aragonite is based on aragonite sand, which has a lot more surface area that slab surfaces. Also, aragonite does not begin to dissolve until the pH falls below 7.7 and calcite does not begin to dissolve until the pH falls below 7.4. Normal reef aquarium pH is 8.0-8.4.

It's possible that the pH could drop a little lower deep inside a sand bed such that it might actually fall below 7.7 during the night for example but only inside the sand bed. These claims may very well be overstated to the point where they are more advertising hype than reality. The only way you could tell would be to very carefully measure the volume of aragonite sand in a controlled tank at the start of an experiment and then re-measure it a year later to see how much, if any, had dissolved during that time period.

Obviously there is zero buffering if the aragonite, or calcite, doesn't actually dissolve. And even if there is a certain amount of dissolution inside the sand bed, assuming the pH is low enough, one must take into account the amount of immediate reprecipitation that will almost certainly take place.

If the pH in your tankwater is low enough to begin to dissolve calcite (below 7.4), then your tank is in big trouble.

In other words, there will be zero buffering from slabs of calcite. They shouldn't do any harm provided there are no undesirable impurities. If the travertine is anything other than pure white, it has other minerals in it. Obviously any traces of copper or aluminum would be very bad for a marine aquarium. Iron, which gives the travertine a beautiful golden rust coloration, would simply fertilize the phytoplankton and the macroalgae.

[mappa]

Thanks Ninong, very informative information. I placed in the tank last night, creating a little haze from the movement in my sump etc, but today coming home the tank actually looked cleaner than it ever did and the fish look unaffected so far. I used the lightest color travertine on the market, so it should be relatively safe with no rust or dark colors like some of the varieties. Thanks again-Shane