It's normal for the stuff to darken after the bottle has been opened, and it doesn't affect developer activity.(posted 8608 days ago)I use Rodinal 1:25 with HP5+ (Ilford's equivalent of Tri-X) for about 90 percent of my shooting. Grain is more apprent than with other developers (D-76/ID-11, Xtol), but there is a greater overall impression of sharpness.