Pool filter sand is awesome, If you have a provider in the area look for 3M Color Quartz. I use white poolfilter sand and it doesnt get stirred up at all really.
You can add it with fish, but its best to do it without.
Nope not at all. Finer sand will, but this stuff is pretty heavy. I try to stay away from the powdery sands. I can stir mine up and it does nothing to the water. Make sure if you get pool filter sand it has no chemicals added, and is not too sharp.
I sgree 100% with Andres... I've tied a lot of different substrates and large grained sand is by far the best... and Pool Filter Sand is the best qway to get large grained sand...
I would remove the fish during the swap. This is more so to prevent stress than anything else...