Those ar ethe JBL balls i use.
JBL The 7 Balls are pressed fertilizing pellets, enriched by a special process with all the nutrients vital for aquatic plants, especially iron and trace elements. The nutrients are released slowly, providing a very favourable depot effect. The ball shape permits the convenient use in existing freshwater-aquariums. Specially suitable for the specific nutrient supply or post-fertilization of aquatic plants which mainly absorb their nutrients through the roots, such as echinodori, cryptocory-nae, and others.For long-term root fertilising in an established aquarium.
Does not contain phosphates and nitrates.
Contains iron and minerals in a form readily accessible for plants to absorb through the roots.
Depending on size of the aquatic plant, press one or more balls into the ground around the roots. Repeat after one year.