Yes, overwatering is very probably the reason this started. As well as over feeding. Don't they recommend you start with two teaspoons per gallon
Need to let the soil dry out between waterings. Should start feedings at a quarter strength recommended and step up after observing your plants reaction to the last feeding.
If your pH is wacked then you will get nute lockout which will further your problems so now you need to find some pH down to get it back to manageable levels.
If it were me I might seriously consider a flush and transplant to try and push the restart button, but that might not be good advice, just what I would be considering.