Measure out the required volume of water into the container.
• Sprinkle onto the water the required amount of granulated agar (20 g per litre).
• Heat the water and stir until the agar is completely dissolved.
• Weigh out the appropriate amounts of phosphate and/or nitrate and add to the warm
agar solution. Heat and stir until completely dissolved.
• Bring the mixture to boiling point then allow it to cool down before pouring into the
jars. If it's too hot the jars will buckle and collapse.
• Fill the jars to the brim. The growing surfaces for periphyton (filter papers) need to be
in contact with the agar.
• Store the filled jars with their lids on in the refrigerator.