|PRIME by Seachem|
|ULTIMATE by Hikari Sales USA, Inc.|
Although both work well and I highly recommend them, my choice is PRIME due to its economic usage. A 16.9 FL OZ (500 ML) bottle of PRIME will treat about 5000 US GAL (18927 L) of water. Whereas, 16 FL OZ (473 ML) bottle of ULTIMATE will treat 960 US GAL (3634 L). Although the initial price of PRIME could be higher, the cost per water treatment is a bargain.
Quick tip - to easy dose water conditioner I use syringe with 10 ml capacity.