Sifting rocks from Oldcastle/Southdown ?

[skyfireblaze]

I first set up my 37g tank in Jun/July 2004. About that same time, maybe a month later, I conveniently had a business trip to Rhode Island. So I figured this would be a good opportunity to go hunting for some Southdown/Oldcastle sand. Sure enough, I found some Tropical Play Sand by Oldcastle at a Home Depot in the area. It's the stuff in the blue and clear bag with red lettering and picture of the boy on it. Anyways, it seemed like it was the right stuff. So I load up about 150 lbs of the sand into three extra suitcases I brought along. The airline employees were hilarious as they checked my bags.

Of course I didn't use it all in my 37g tank, so I've had a big bucket of sand stored deep in a corner of my garage. I know for a fact that it's sat untouched these last two years. Well I opened it last night to use it and realized that there were a number of rather large stones, rocks, pebbles, etc. mixed in with the sand. And yes, it was like that out of the bag. So it looks like I need to sieve through the sand to get all the big stuff out. I remember doing this a bit when I first put it in my tank 2+ years ago, but the rocks I saw last night were bigger than I remember. But still, it's been two years ...

So my question here is this ...
Is this sand really the right stuff? Should I really be needing to sift through it all to get these rocks out? Is the true Southdown/Oldcastle sand supposed to be like this?

Also, I tried to do the vinegar test on it and yeah, it bubbled up a bit. Not like baking soda and vinegar, but still more than what you'd get with an inert or silica sand. Still, I guess I'm not completely convinced by my vinegar test since I've never tested "true" aragonite ...