I used to do that. The gray is IMO suspended silver particles. Given enough time, they will settle. I used the stuff until I began to feel guilty about the color, then mixed a new stock. Old custom was to add a certain proportion of "seasoned" stock to the new batch. Part of the change when using replenishment is the build up of bromide in solution. This was actually considered desirable in those days up to a point. If the particles get to be bigger than colloidal, you can filter the solution, but those should settle fairly rapidly. Just don't stir them up when you pour into the tank. Replenishment was used mostly in large tanks for sheet film in hangers, where there was no pouring from one container to another. Quite a sludge could accumulate at the bottom before a new batch would be mixed.