The answer to play sand vs aquarium sand is being pushed as the play sand is fine for everyone. I'm not one to make statements without checking a little more thoroughly, or at least I don't like to just spew hearsay, as good as it may sound, particularly when there is some doubt cast on the "apparently blatant obvious answer". So I thought I would look into this closer and see if it is really as easy as stating that play sand is fine... period. Usually things aren't always so cut and dried and it turns out this s no different. The hints that all is not sunshine and roses in Playsandville
Someone mentioned a failed vinegar test for sand the other day, Byron said that he wouldn't use anything labelled as "beach sand" just in case, sand packagers (some, I haven't checked many) label their sand as "lake sand" so it refers to being "suitable for use as beach sand" and I've noticed more white (not quartz white) on the surface of my sand lately. Vinegar test
I decided to try the vinegar test on my sand, I happen to have about a cup that I did not put in the tank... now I know why. I placed a tablespoon of sand in a bowl, added vinegar to cover the surface and watched. There were tiny bubbles that were only noticeable under magnification, but they were there. I went digging to the source of the bubbles and found, to my surprise (although I probably shouldn't have been) found little pieces of shells. Shells in my tank
Shells, being less dense than sand, will tend toward the surface when immersed in water and agitated, which is what I am seeing in my tank. The trumpet snails are stirring things up and the shell pieces are the white that is appearing on the surface of the sand.
Attached is a picture of the bowl after the vinegar has mostly evaporated away leaving an obvious calcium deposit (CaCO3, calcium carbonate). The acid in the vinegar dissolved the CaCO3 (shell material) and left it behind as it evaporated. Removing shells in the rinse cycle
I expect that, due to the less dense shell material and the larger size of the shell particles that I could have rinsed most of them out of the sand using a continuous flow technique rather than the fill, stir and dump method that I used. I'll try this for my next tank...
. This might actually be easier to perform and was hinted at by someone here but the benefits were not mentioned other than it just working for them.
Sand in bucket, hose in sand, turn on full blast and make sure that the hose stays at the bottom. Just let it overflow until clear. Probably best to use a shallower bucket and/or a taller one with a few 1" holes in the side 1/3 the way up... testing needed to see at what level the shells will get to given the water volume flowing. OK... is this really a concern? Tap water
I had my water professionally tested and the results were 23dGH, 21dGH and 7.78 pH. These were tested by my API test kit just to verify the kit findings, they were close other than my pH resolution showing 7.8. Tank water
After a little over a week of plants and fish my tank was sitting at 17dGH, 14dKH and 7.8 pH.
After three weeks total and one week since my last 30% water change using my hard tap water my parameters are sitting at 18dGH, 14dKH and 7.8 pH (interestingly 8.0 right before lights out... but that is another topic)
I would say "obviously" the sea shells are not causing an increase in my KH but that may not be true. They may very well be holding the value higher and I would have no real way of telling short of letting this go for another month and replacing the sand, then comparing the findings... but that could be less than conclusive due to tons of factors that I am not controlling directly.
I suppose that I could create little bottles of "sand only" samples and sift out all the shells in only one then do some testing over time and see how much of a difference this can make then extrapolate the results into 37 gallons. Maybe another time. Conclusion for me
My conclusion is that I am not worried about the shells at all due to the obvious KH reduction in the tank environment. Whether this is due to plants, driftwood, water chemistry itself...perhaps the higher pH, fish... I really do not know. I selected fish that were good in higher GH water, some up to 20 and some up to 30, figuring that, worst case, I could add some reverse osmosis water to reduce the hardness as needed. I may not even need that even with the shells. Should this be a concern to anyone else?
I suppose different sand will have different amounts of shell material, after all, lakes have shells in various quantities. In a case where someone needs really soft water, my unknown KH affect could be cause for concern. Perhaps it adds one or two degrees, perhaps it is negligible given the seemingly small amount of shell material. I would go so far as to say that in any similarly planted tank (number of plants relative to tank size) it is probably not an issue if the fish tolerances allow for room in the water parameters in the first place... and they should as trying to keep fish at the outer boundary of their tolerance cannot be good for the long term health of the fish. Vinegar test revisited
Perhaps the vinegar test should not be a "go - no go" test but a relative test to determine how much bubbling occurs and gauge whether to use the sand based on the anticipated water requirements relative to the fish. If the bubbles are few and small (need some magnification to see them) or are vigorous, large and many (plainly seen)... obviously not a defined measure... you can decide how much variance your system is likely to tolerate... or you can just buy aquarium sand and not worry about such mundane things as testing, thorough rinsing and verifying what the sand source may be.
I included a tank shot for reference.