Yellowing leaves (entire leaf) indicate nitrogen deficiency when it
occurs in new leaves. Streaked or mottled yellowing (in between
veins) indicates iron and/or manganese deficiencies. Add nitrogen to
the substrate (try to avoid using products with phosphorus) for the
former, lower pH for the latter.

jammer j@mmer wrote:

My water lily went from 5 to 14 leaves in no time. Then a baby pad was
yellow so i picked it off. Now 2 more are yellow. Everything else is
fine and thriving. What do i do!!??