TLDR: My main question is, how can I speed up Fluval Stratum losing it's buffering capacity? My PH is dropping too low and I would like it to settle as fast as possible. My only concern is not stressing my plants too much. More details below.

I started this tank on April 6th and have been struggling to get it cycled and keep the PH from dropping. I used alot of fluval stratum as the base of my substrate and capped it with Caribsea Eco Complete. There's also a significant amount of Mopani driftwood in there and I think that, in combination with the fluval, is buffering ph way too low.

My tap water is PH 7.5, GH/KH both at 3. I have done a large water change about once per week since starting the tank, but PH drops back to mid 6's in just 8 hours and eventually will drop below 6. I used Turbostart 700 to begin the cycle, and have been dosing Seachem Stability daily per instructions. There is no livestock in the tank yet.

I've been dosing 2ppm Dr. Tims Ammonium to feed the bacteria. After 24 hours most of the ammonia and nitrite have converted to nitrate, but there's still just a trace amount of both that linger at just under .25 ppm. I'm assuming the bacteria are struggling to complete the process because of the low PH.

What process can you guys recommend to help the ph buffering wear off faster? I'm committed to this scape and definitely not willing to pull the stratum out. I've read some will use crushed coral to temporarily balance PH, but I've also read some say it's a bad idea. Are regular water changes and waiting the only safe option? Any suggestions are appreciated.