PH, dK and Calc Problems.. any help would be nice!

[RyanJ]

Hey there guys.. So i have a slight problem with my water.. If anyone has experienced this please let me know what you did to fix it!
My PH is 8.0 But my dK is close to 380 mg/l (21.0 dHK) and my calcium was < 300ppm I have corrected the calcium.. but I have no idea how to bring down the dHK.. Dose anyone know how to bring this parameter down?? without causing a huge PH issue??
I have heard the Carbonated soda will drop the dHK.. But wont that effect the PH as well??


Tank Info
125G FOWLR tank & a 15g nano.. on the same system!
PH 8.0
dHK: 21.0
Calcium: 450ppm Was under 300PPM but adjusted!
I haven't tested the rest in ages..
What started me on this wonderful adventure, I bought a Neptune apex and i have been trying to Get my PH to 8.3 using eight.four from aquavitro (Seachem) And Balance, Witch is meant to bring up the PH without effecting the dKH... But When i get it to 8.3, it drops right back down to 7.5-8.0 overnight! is there anything im missing here???

Thanks for the help guys~!!