Aquatic plants obtain the nutrients they need for healthy growth from their environment and the organic and mineral particles deposited there and in the water. The most important elements are CO2, potassium, iron and phosphorus. Metabolic products of the aquatic fauna play an important role here. Animals, water and plants should establish an optimal balance in a well-adjusted tank. However, discoloration of aquatic plants can be an indication of disturbances in the nutrient balance. Often, freshly planted plants lose all their leaves initially because they have been pulled above water. You can fill in the gaps in the supply with a CO2 system and/or special fertilisers. A brownish discolouration of aquarium plants is an indicator of iron deficiency. Iron fertilisers can help. Yellowish-waxy leaves indicate potassium deficiency.