Is your dining room on a concrete slab? If not you're going to need to reinforce the floor joists to withstand the weight of the tank, and that's something you should ideally do before even moving the tank into place, and absolutely has to be done before filling it.
The easiest way to do that would be to put some of those adjustable floor jacks underneath the corners of the stand and under the center supports in the stand. I'd recommend getting in touch with a contractor or ideally a structural engineer to figure out exactly how much support you need, because 500 gallons of water entails an enormous amount of weight.
Things will get extremely complicated if this is a second floor; sistering joists and carefully positioning the tank might be able to get you sufficient floor strength, but you'll also need to consider the load on the structural beams as well at such large volumes.
The easiest way to do that would be to put some of those adjustable floor jacks underneath the corners of the stand and under the center supports in the stand. I'd recommend getting in touch with a contractor or ideally a structural engineer to figure out exactly how much support you need, because 500 gallons of water entails an enormous amount of weight.
Things will get extremely complicated if this is a second floor; sistering joists and carefully positioning the tank might be able to get you sufficient floor strength, but you'll also need to consider the load on the structural beams as well at such large volumes.