[harris51]

I have a curious situation.

My 3+inch deep argonite sand bed seems to be constantly "off gassing" tiny bubbels. At first, I assumed it was Nitorgen gas finishing my denitrification.... although I admit this is my first DSB tank so I don't really know what to expect.

However, the volume seems excessive. As a hemit crab walks accross the DSB you can watch him trail a line bubbles.... it is quite impressive. They almost look carbonated

Could this be something else? Could it be CO2 from argonite buffering???

I have no bubble producing powerheads or other source of bubbles and they are very fine boubles clearly being gently produced by the sand until disturbed.

73 gal. bow 7 month old reef with parameters = Sal. .025, pH 7.9-8.2, Trace nitrates, 0 phos., Temp swings from 78-82 from 2 MH and 4 Actinic. I am still recovering from a 600+ calcium swing from a rogue seachem block.... not sure if that would play a role?

Any thoughts?

[Ninong]

I wouldn't be concerned. Could be N2, could be N2O, could be O2. It's not CO2, because CO2 combines with H2O to form H2CO3.

[harris51]

I agree it is not likely CO2, however, since I havn't added any of my two part buffer/Ca in a few weeks.... re: Calcium spike from "the devil blocks".....

I thought maybe the argonite could be disolving and off gasing?

Glad to hear you think it is nothing to worry about.

Thanks

Skip

[Ninong]

Originally Posted by harris51

I thought maybe the argonite could be disolving and off gasing?

The gasses (N2, N2O, O2) that are produced in a deep sand bed are the byproducts of metabolic processes, not the dissolution of aragonite.

The extent to which aragonite dissolves in a deep sand bed is an extremely complex chemical question. Factors that have to be taken into consideration include: pH, salinity, temperature, pressure, saturation of the water as respects calcium carbonate, etc. Natural seawater is supersaturated as respects calcium carbonate. The water column in a typical well-managed reef aquarium is almost certainly supersaturated.

For example, aragonite doesn't even begin to dissolve until the pH falls below 7.7, which is not likely to happen in the water column of a well managed aquarium but it could possibly happen in the micro-environment surrounding each individual grain of aragonite sand in a deep sand bed thanks to the metabolism of bacteria lowering the pH in the immediate micro-environment of each grain of aragonite sand. However, I have been told that we need to take into consideration the potential for reprecipitation of this dissolved aragonite which may result in an insignificant amount of net dissolution. In other words, when I argued that it is possible to measure pH levels below 7.7 in a sufficiently deep DSB which I assumed would lead to dissolution of aragonite, I was informed that I was ignoring the fact that most of this dissolved aragonite would immediately reprecipitate.

I no longer express an opinion one way or the other on the potential for aragonite to dissolve in a typical reef aquarium with an aragonite sand bed. I believe that it probably does dissolve to a certain extent but I have no idea whether this amount is significant or even measurable. That would be a good science project for an enterprising young high school genius.

[harris51]

Excellent and balanced explanation.

Thank you