Complex sentence: Over 6,000 animals are housed in the oceanarium which contains 1.75 million litres of water pumped from Darling Harbour, filtered and heated before it flows into the Oceanarium and adjoining display tanks.
Split into simpler sentences: Over 6,000 animals are housed in the oceanarium which contains 1.75 million litres of water. Water is pumped from Darling Harbour, filtered and heated before it flows into the Oceanarium and adjoining display tanks.