Simply Koi and More Koi

At the moment everything's hunky dory in my small heavily stocked mature pond but I want to stay ahead of the game and am considering adding a few more litres of K1 in my Nexus to increase the biological area.
How will this impact on what is already a fragile eco system?
At present I add around 400g of sodium bicarbonate a week to maintain a KH above 3° (1500 gallons heated) the KH can drop right out in a week if I don't add it.
My readings are stable and constant as follows
PH = 7.6
KH = 4°
GH = 11
NH3= 0
NO2-N = 0/ 0.25
NO3-N = 10
12 of my Koi are between 60/80cm and one new addition is 30cm all are still growing hence considering more K1.
A new 4000 + gallon pond is on the horizon but it won't be ready for a couple of years at best.

hi and welcome

I don't think extra K1 will help with stocking that high, and im not at all surprised your kh is suffering, your best bet is to supplement with a shower
either that or thin some of these out or start that pond ASAP

duncan