it depends on what you have stocked in your tank....if you just have liverock, you don't need any supplements if you keep up with water changes..they will replentish your trace elements....for calcium, i use Purple Up or Aragmilk....i don't use anything else....if i need to slightly adjust the ph, i use Kent Superbuffer DKH...if your ph is severely off, i would do some large water changes......don't overdose your calcium though...i use about half or less than the instructions on the "Purple Up" say to use... this stuff works great..lots of corraline!!