sea shells, sand and alkalinity as it pertains to hardness - Page 2 - Tropical Fish Keeping - Aquarium fish care and resources
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post #11 of 14 Old 02-01-2013, 09:07 PM Thread Starter
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The final prove is in the pudding.... or the pudding bowl anyway.

Preliminary results indicate no shells, couldn't find any in a tablespoon rinsed sample but lots of black and dark grey stone which does not look like quartz. I suspected limestone.

Added vinegar. Lots of bubbles, more than with my shell sand but it's been a while since that test so that's hardly an empirical measure... although I was surprised at that.

Sorting through the grains to determine exactly which ones were bubbling revealed that the black and dark grey stone pieces are the culprits, limestone. Seeing as limestone is mostly some form of calcite which is primarily crushed skeletons of various sea creatures, probably anything from corals and whatnot.... it might as well be shells, just a heck of a lot older.

Recall the 99% to 99.9% pure silica quartz by weight? I would be surprised if it was as high as even 99%. I left the sand and vinegar in a bowl to evaporate overnight, basically the same as I did testing the sand that I used.

Pic one is my sand.(source uncertain, Home Hardware supply)

Pic two is the Quickrete Play Sand.

I was surprised yet again as there was far more deposited than I anticipated. While I am not trying to prove one sand source is better, I thought it prudent to point out that both are similar with regards to there being calcium content. If I were trying to prove anything beyond this, I would make certain that the comparison was more empirical and include other sources while I was at it.

So if you really really need to eliminate any form of calcium source from your aquarium I guess your best bet is to avoid playsand. I might do a test with water sometime and see how much, if any, calcium is deposited.

Seeing as many here have used it for many years with no problems I see no reason not to use it for the vast majority of tanks. I actually see the KH remain constant or drop very quickly after water changes, I have not figured out the process behind the drop yet but obviously the calcium in my sand seems to have little bearing on this.

Attached Images
File Type: jpg CaCO3.jpg (21.4 KB, 16 views)
File Type: jpg Quickrete Playsand calcium.jpg (40.7 KB, 16 views)

Total years fish keeping experience: 7 months, can't start counting in years for a while yet.

The shotgun approach to a planted tank with an LED fixture

Small scale nitrogen cycle with a jar, water and fish food; no substrate, filter etc
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post #12 of 14 Old 02-17-2013, 06:41 PM
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this piqued my interest, so I did an experiment as well

started with this:

and since I didn't have sand guaranteed to only contain SiO2, I instead compared the play sand as it is straight from the bag to some that was altered to contain at least 1% CaCO3, using this:

since vinegar was used before, I chose this:

and for futher comparison:

I looked at two things: 1) gas liberation/solid formation and 2) impact on pH

next post will show the results of the former
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post #13 of 14 Old 02-17-2013, 07:16 PM
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here I took two samples of pure play sand and one sample of play sand, which I altered to 99%/1% CaCO3

to one pure sand sample I added approx. 1 mL HCl and to the others approx. 1mL Acetic Acid, then to each was added approx. 25 mL of RO/DI water

observation: no gas liberation in the samples with no added CaCO3, lots of bubbles with CaCO3


waited a little while and stirred the mixtures and checked the pH of each, still no bubbles in the first two, and though it doesn't really show in the photo, was still getting some in the third, pH was as follows: HCl - 1, Acetic/pure sand - between 2 and 3, Acetic/99% sand/1% CaCO3 - about 5


next, I dried the samples

observations: slight discoloration and crust formed with HCl, no solid formation; similar crust but no color change and no solid formation with the Acetic/pure sand (the 'crust' was easily broken and did not represent precipitation of solids from the solution); white crystal growth (calcium acetate) on surface of the Acetic/99%sand/1%CaCO3


next post: pH
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post #14 of 14 Old 02-17-2013, 07:29 PM
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for pH, I used 50 g pure sand and 50 g of the 99%sand/1%CaCO3 mixture, placed in a beaker to which approximately 200 mL RO/DI water was added, then I checked the pH of each over the course of a couple of hours, results as follows (pure sand on left, sand/CaCO3 mixture on right, pH measurements taken at about the same time):



observation: little change in pH in the pure sand sample, steady increase in pH in the sample with added CaCO3
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