As long as it is a cation it should be held onto by the Akadama. So Mg++, Ca++, K+, NH4+ etc. There are varying degrees that each will be held though. Anions like NO3-, H2PO4-, Cl-, etc won't be touched by the Akadama.
Tap water mainly contains the cations we want, ie, Mg++, Ca++, K+ in varying...