Opportunistic feeders, their diet varies from one region to another. In the Antarctic, killer whales eat about 67% fishes, 27% marine mammals, and 6% squids. Killer whales in the Bering Sea (near Alaska) eat about 65% fishes, 20% squids, and 15% marine mammals.
Even though your shower grout looks dry, using it too early or sealing it before it's ready may damage it, leading to premature failure. Most cement-based grouts require a cure time of 48 to 72 hours before applying a penetrating sealer.
Now I suggest to people to NOT SEAL grout. If you use Stain Solver, a Certified organic oxygen bleach, it will remove any stain from grout in minutes. After the grout is dry (three to five days), seal the grout with a silicone grout sealer. These products are available at your tile supplier. Be careful not to get these products on the tub or shower floor, as they are very slippery. The grout needs to be sealed, as it can and will absorb water.