most common ones are rhodamine WT (Fig) and fluorescein (C20H10O5Na2)
Ho and Houghton at LDEO performed a comparison of SF6 and fluorescein in the Hudson River and found that fluorescein became undetectable within 4 days. 36 kg of fluorescein and ~4.3 mol of SF6 were injected into the Hudson River at an averaged depth of 9.5 m, ~1 m above the bottom, near Hyde Park, N.Y.