Join Date: Aug 2012
Location: Ann Arbor, MI USA
Not sure if it actually important or not, but if adding directly to tank it says to treat the entire tank volume rather than just the volume you are replacing.
" May be added to aquarium directly, but better if added to new water first. If adding directly to aquarium, base dose on aquarium volume." - from Seachem website
Oh and I should add, I have been doing this for years as well and never had an issue. I slowly fill over a few hours.