New tank ph swings

[DrBoxedWine]

My qt stated cycling about 8 weeks ago, it's been fully cycled for about 2 weeks. My ph seems to swing by letter 7.8ish and maybe 8.5ish? The api tests are not the most accurate (I need to get some better ones). My kh is about 13-15 (again, stupid API test). Is this normal? I'd like to get my first fish, but i'm worried about these swings...

 

[thegrun]

If those swings are real they would likely cause problems. What salt mix are you using? 13-15 dKh is definitely high for alkalinity.

 

[DrBoxedWine]

I added a tablespoon or 2 of baking soda in the past few days (kh was around 5 before), maybe I added a bit too much. Would a water change be necessary? I may need to get better tests.