Fast addition generally gives slower speed and higher contrast, whereas slower addition tends to increase speed and lower contrast. Just a very rough generalization.

If you use chlorine in your water, it will add a small amount of chloride to the emulsion, but that is probably insignificant. If you have ozonolosis, I have no idea what it will do.

Acid tends to increase contrast slightly with some emulsions and alkalinity tends to decrease contrast and speed up hardening. It decreases the lifetime of the melted emulsion with hardener in it.

Pepper grains, or black specks in your prints is from large grains which aggregate. It is usually due to not having enough or good gelatin. I never got it at Kodak, but I see it here with different gelatins or different batches of the same gelatin.

Your only recourse might be to dilute the silver more or add more gelatin. But, that might create other problems. The emulsion would become too dilute or too viscous.

PE