Though natural sea water has a major constituent of phosphates, they are of no good in a closed reef aquarium setting. Even if phosphate is present in a reef tank in low concentration, they can spur algae growth and slow coral calcification. If by chance their concentration increases in a reef tank, algae can enormously capture the aquarium and corals can virtually stop growing, and even start to recede. When you are shedding bucks on getting algae removed from tank, it is important that you check on the reason behind their growth. It is most probable that you tank has phosphates that are inviting the algae to dominate your tank.