Same issues here when I first started Ara-290
It does require PBS, I use 1ml of it to dissolve, then 1ml bac.
As others mentioned, you can add baking soda to bac but not sure how to do that and keep sterile.
I found a PBS supplier of sterile water online, Google PBS for labs.
Search for them and order online.
Been using for many months no issue. I keep bottle in dark closet, not in refrigerator.
Make I wipe cap and neck with swabs each time.
Also make sure the ARA and PBS are room temperature before you mix. It's very sensitive.
Good luck.