hiya don't be a cheap ass,lol none of them really work proper check ya water and if it as an high pH above 7'ish use that as ya pH up if it's lowbelow 7 you can use it as ph down..so ya only need 1 of them thats what i do.......if ya ppm is t high add water and it comes down if it's too low add nutes till ya get ya desired ppm..it go's up..gluck