not much clawing, so not 'incredibly overfed' ... happened slowly, which is good too. Any change will likely need to be subtle and small.
I'm not familiar with biobizz, but if they have guaranteed analysis labels you can calculate ppm of each nutrient. good can help find a calculator for you. since it is liquid, you my need to account for specific gravity.. depends on unit they used. Assuming it is coco/soilless substrate?
First, ensure pH is somewhere near 6. runoff is not highly accurate, but can inform if it is drifting one way or another relative to what you put in. That is usually enough to eliminate it as a possibility. A slurry with some substrte mixed in with a known pH water can work too... if you do that, use same volume of water and substrte in future for the slurry, so you can build some familiarity. Again, not very precise, but will tip off whih way it is drifting and magnitude.
i have similar hard water.. here's what i typically use with a 2-part mix *3 with epsom salt i guess.
With pH 6ish... just as important as concentrtion of nutes
120ish N
50ish P
200ish K
100ish Ca
80ish Mg
110ish S
hydro nutes should have all your trace elements too. most are a fraction of 1 ppm. each week in just about any of my diaries you can find a table with these values. These are all "ballpark" values.. your tap could impact what is right, too. A rare plant is a picky eater, too. ~1.5EC is a good target (or ~750ppm). with my hard water i am around 1.3ec with no problems. i start going higher and get 'the claw'.
if not wrong about 'soilless' coco substrate, make sure you get 10-15% runoff religiously each time you irrigate. Always fertilize. in soilless you maintain a fertile substrate at all times with a known concentrtion. the 10-15% runoff maintains those concentrtions and therefore the pH too -- excluding outside factor like microbes.