KNO3, KH2PO4, K2SO4, CaSO4. MgSO4 and a carbonate (optional K2CO3). Micro mixes come in several variates. They are all dirt cheap, last a long time and just need a set of small Teaspoons or gram scale.
You can dump them in dry or make your own solution. I’ve done both and recently make my own solution. It’s just too easy to squeeze a bottle and dump it in.