The DSR method is really interesting. I’d love to try it myself, but that takes precision and near daily readings.Like others have suggested I think a few large water changes will be the best way to get your parameters back on track. Once you do you will need to dose a lot more than just ALK, Ca & Mag. It is not that hard, but you need to know where you stand so you can figure how much of what to dose. The ICP tests can be a big help or you can buy additional test kits for the most critical elements.
You may want to look into the DSR method. There is a thread here on it. I find the spreadsheet is very helpful in determining what and how much to dose. It takes a little while to determine how much you need to dose the different elements. I have not done a water change myself in close to 3 years myself.