One alk swing will not usually do this... it has to be constant inconsistency.
If your tank is less than a year old, then you just have to wait. Nobody wants to hear this, but there is no getting around it, really. ...even the people that think that they have stable young tanks are kinda fooling themselves a bit and even comment later that they had no idea what they were talking about now that their tank is older and more mature.
Yes, keep everything stable. While parameter numbers do matter, consistency is probably more important than any one value (until/unless you are wanting to specialize).
These can sometimes grow back, but not always. If it is point-source shading, then it will get worse and probably not have much chance of growing back unless you change the lighting.