Do you have the scientific (latin) name of the umbrella plant? It may be that it is not a true aquatic plant.
If you determine that your plant is indeed aquatic, then consider the possibility of lack of available iron. Leaves usually turn yellowish due to this. As a rule of thumb for aquatic plants, chelated iron supplementation (as in feeding or fertilization) is desired and not harmful for fish.
There are two main ways of dosing iron: by adding it to the water (say weekly or even daily) in prepared products that can be liquid or in tabs (such as
API Leaf Zone or Tetra FloraPride to name two) or by using enriched soil-based substrate (either by preparing your own soil -not recommended; or using commercially available nutrient rich substrate, such as Eco-Complete or Azoo Plant Grower Bed, to name two).
That said, I have found that some of the plants that are sold in the plastic vials are not true aquatic plants.
Pepetj
Santo Domingo