NPT means Natural Planted Tank-- I think.
I just just "Googled" Toronto/geology/limestone and found several discourses on limestone (see paragraph from one document below), so I would assume Toronto, unlike Southeastern USA, has plenty of limestone. I know parts of Kentuckky, Wisconsin (and now SW Ohio) have hardwater and thus, probably limestone deposits. Something about glacier activity? The Southeast where I live is ancient and well-weathered plus the glaciers didn't get down this far south.
My
Rocks and Minerals book says that vinegar works on powdered limestone. Just a few minutes ago I put a piece of coral into pure vinegar and it started to slowly dissolve releasing little crumbs and a tiny bubbles. With a stronger acid, it would surely fizz.
Of course, even in a limestone area you should find plenty of non-limestone rocks-- dark grey basalt, whitish quartz, etc.
Rocks formed millions of years ago, before human pollution. So if you find a rock in a polluted place, it should be perfectly fine. Just give it a quick scrub to get off any outside goo.
PARAGRAPH FROM ARTICLE ON TORONTO AND LIMESTONE:
In southern Douglas County several faults and sharp structures have been observed in the Douglas Group and the Oread Limestone. Rich (1932a) first described these features as follows: South of a curved line marked by sharp flexing and faulting, which for several miles of its course closely follows the northern arc of a circle of about a 4-mile radius, the Toronto Limestone is missing; the Leavenworth Limestone is thicker than average and the Heebner Shale is abnormally thick, 16 feet instead of 6. The Plattsmouth Limestone at several places along the arc was faulted so that south of the fault it lies at the same level as the Toronto Limestone north of the break. These relations indicate (a) uplift of the area south of the curved line so that the Toronto either was not deposited or was eroded after deposition; (b) a renewal of movement, causing a relative sinking of the area south of the fault line while the Leavenworth Limestone and Heebner Shale were deposited; (c) deposition of Plattsmouth Limestone over all the area; and finally, (d) post-Plattsmouth faulting with downthrow to the south.