Low KH high GH, pH problems?

I have a cycled medium-planted low-light 10 gallon tank, and I was having some pH problems. I did add driftwood that might've lowered it, but I think very very high nitrates might've also been lowering my pH. I will post my pH log at the end.
I want to make sure my pH is stable before adding one pea puffer to the tank. After testing, I got 3 KH and 9 GH. Is this reasonable? Should I try to lower/raise this? The GH seems a little high and the KH seems a little low from what I read.

ph 4/10 - 7.6
ph 4/11 - 7.6
ph 4/14 - 7.6
ph 4/18 - 7.4
ph 4/21 - 6.6
ph 4/22 - 6.6
ph 4/22 - 6.0
ph 4/22 - 7.0 (after water change)
ph 4/22 - 7.2 (after baking soda)
ph 4/23 - 7.4
ph 4/24 - 7.4
ph 4/25 - 7.0
ph 4/26 - 6.6
ph 4/26 - 7.4 (after water change)
ph 4/27 - 7.2
ph 4/27 - 7.6 (after water change)
ph 4/28 - 7.4
ph 4/29 - 7.4
ph 4/30 - 7.4

My pH has been stable the past few days. How long would you wait before adding the fish if it remains at 7.4?

My nitrates were sky high from around 4/22 till that last water change on 4/27, so I am hoping that might have been causing the pH drops? I have only found two sources online saying that could affect pH so not sure

 

Yes, nitrates do drop pH, since nitrates are acidic. Most of the time it's not enough to change much but if you had a nitrate spike it could have dropped it like that.

 

Yes, nitrates do drop pH, since nitrates are acidic. Most of the time it's not enough to change much but if you had a nitrate spike it could have dropped it like that.

I think my nitrate was 300+ ppm because I was dosing ammonia to 3 ppm every day (and it was converting to nitrate within 4 hours)

 

It's not the nitrate, I have the exact same kind of water, driftwood drops my pH from 7.6 to 6 in a day or two. That's why I put limestone in my tanks to keep them at a stable 7.6 if I have driftwood and want to keep hardwater fish. Eventually the wood will stop lowering pH if you keep it in there long enough though.

 

I think my nitrate was 300+ ppm because I was dosing ammonia to 3 ppm every day (and it was converting to nitrate within 4 hours)

Oh yeah, that would do it. Your PH should be ok now.