3 channel vs 4 channel

[Craigdillman]

Hey just getting into the world of dosing my tank is now exceeding the 2 week water changes and kalk ATO needs so I'm finding my self dosing alk and calcium in between changes along with vinegar, just wondering what else people use a dosing pump for and would 4 channels we needed or is 3 enough? Right now I dose vinegar alk and calcium and like once a month mag but that probably doesn't have to be on a pump