Phosphate has several negative effects if present in a too high concentration. First of all undesirable algae growth might result. Making an aquarium an unpleasant sight. Phosphate also blocks or retards the growth of corals and calcareous algae. One of the scientific studies shows that a phosphate concentration higher than 0.05 mg/L decreases the growth of calcareous algae by 90%.
Salifert Test Kit Phosphate