Instant Ocean Salt, RODI water and Kalk whether it be pickling lime or a manufactures kalkwasser...Basically only things that I have used and need to keep on hand. Alot of people do use 2 part additives, but the kalk will keep your calcium an ph pretty stable especially if dripped 24-7 for topoff....My tank is a sofetie / LPS tank and these items keep it stable....This is just my setup and I am sure every tank is different.