Need a structural engineer

[toxic111]

For what you are looking for, try AMEC earth & environmental, they do concrete testing, check the yellow pages to see if there is one in Calgary.

I have used them in the past for concrete testing on foundations. They would probably be your best bet over a structural engineer (they usally have one on staff anyway)

Based on my experience in the industry, older concrete is on average than the current stuff. If you are looking at a standard basement floor, 180lbs/ft2 is not that much, even with no rebar, a garage floor is the same thinkness, and is holding much more per foot.

One thing to watch for is any existing cracking, that might indicate a problem, or it may not, as all concrete cracks, it is normal.

BTW I have over 15yrs experience in the design & building industry, so I do have a bit of an idea on what I am talking about.

You could also increase the loading by addind some sidewalk blocks under the tank, which would spread the load over a greater area.

Hope that helps some.