One thing to check is can the "island" support this weight ? A mate of mine had a large fish tank between his kitchen and dining room on what he thought was a brick plinth (came with house when he bought it). One morning came down and found a pile of "brick cladding" on kitchen floor and found that tank stand was 2"x2" wood frame structure covered with plaster board and 1/2 bricks cemented on ot look like solid brick The weight of the tank had distorted the frame and/or wooded floor and pulled screws out of the very dodgy wood work frame causing frame to sag.
His solution was do it "proper", brick stacks under floor to support floor joists, then concrete block centre and brick outer layer plinth with a top of re-inforced concrete/cement. Also lowered the tank slightly so as to get easier access to the top for cleaning and room for air pumps filters etc.
All looked fine when sorted. I think the tank was 700l.