Seachem PhosGuard ™ rapidly removes phosphate and silicate from marine and freshwater aquarian. It is not recommended for phosphate buffered freshwater.
Phosphates are present in every aquarium and if they aren't properly maintained the levels will continue to go higher and higher causing algae growth . Phosphates arent directly harmful to your fish but the algae blooms which will occur can deplete oxygen which would then effect your fish . Phosphates naturally occur as wastes are broken down within the aquarium but can also be added as anything from food , chemicals to buffer water and the actual water could contain phosphate.