Hey bro,
I believe the value of KH cannot be taken as a sole reading itself. It should be maintain in relation to the other 2 critical value like pH & Ca.
If KH is high>10 and a high pH>8.5, it is not possible to maintain a high calcium level as most of it will be precipitate out from the seawater.
Natural seawater have a KH of 6. IMO, a KH of between 8 - 9 should be good. I maintain mine at 8. All in all, i believe it is he delicate balance of the 3 component together rather than getting the values correct for each individual..
Just my 2ct... u may disagree...