The whale brush has been a life saver. I can not imagine people who forget whether they had to go through the twice a day brushing. I will never forget!That is some awesome looking tile! And I love the marker tiles. Never seen them before. However, you should get fined for gratuitous placement of a wall whale brush in a photo.
Depending on the construction of the pool the gap can be an expansion joint that needs to be left open or filled with flexible mastic. Putting in solid grout will cause cracking as the pool structure and the deck structure move independently.out of curiosity and ignorance, why wouldn't you grout between the coping and deck?