should I e worried aout y floor?

[Myka]

I'm a carpenter, I should be able to help you out.

Which way do your floor joists run? Do they run parallel with the length of your tank, or perpendicular with the length of your tank? If the floor joists run parallel to the length of your tank, then your tank will likely only be on two floor joists (assuming you're tight with the outside wall), and that would not be good. A 220 gallon tank filled with water and rock weighs roughly one metric tonne. That is a lot of weight to put on 2 floor joists. In this case, I would get the floor reinforced by a professional.

You want the floor joists to run perpendicular to the length of your tank as your tank's weight will then be over several floor joists. If your floor joists run perpendicular to your tank's length, and your tank is sitting against the outside wall of your (single family) house, then your tank is sitting on the strongest point of the floor joists as the ends of the floor joist will either sit right in the concrete of your house's foundation, or right on top of it. In this case, your floor should (I say this only to protect myself haha) be able to handle the weight.

Btw, concrete is the hard stuff that steps, foundations, side walks, etc are made of. Cement is that powder stuff in a bag.