I presume by 'normal Roundup', you mean Roundup 360gm/l glyphosate concentrate and not one of the 'premixed' Roundup products ...
That said, both normal and Biactive Roundup contain the SAME amount of the SAME active ingredient.
The biactive formulation had different surfactants / wetting agents that have less impact in aquatic and near aquatic situations (eg harm to frogs).
Check / compare msds for more info.
To quote from the manufacturers info
"Roundup BiactiveŽ has been specifically formulated for use in environmentally sensitive areas. This unique formulation contains an 'aquatic approved' surfactant, allowing for use in sensitive areas such as around streams, creeks, dams, channels and drains. Roundup BiactiveŽ controls a broad spectrum of annual, perennial and aquatic weeds."
Don't know why you are seeing a difference except maybe you are dealing with some 'hard to kill" weeds and need to add wetting agent or penetrant (eg pulse) to make your roundup mix more effective.
Joe