(a) NO. The table will support a little over 3 ft³ of water. The volume of the aquarium is (3 ft)³ = 27 ft³, substantially larger. Hence the weight of the filled aquarium is substantially more than the table can support.
(b) NO. The density of water (mass per volume) at a given temperature is substantially constant. That is, water is regarded as an "incompressible fluid." (Water does compress so that its density increases very slightly at extreme depth, but the effect is not measurable over a depth of 1.5 to 3 feet.) Temperature has a much greater effect on the density of water than does depth.
