What's up bro! I started using that stuff after my Taiwan breeder told me that's what he uses on all his tanks exclusively. That alone means A LOT! Ever since, I've been using it for all my tanks and they're doing awesome. I've been letting people know about it and many folks have had positive results with it as well. Only cost $16 on Amazon for a 500ml bottle so it's hella cheap!
Sucks you lost that beautiful Black Impact momma.
You should've redid that tank a long time ago bro... live n learn though. We all do.
You're RO ph seems normal. What's your RO TDS?
Once you start using ADA AS accompanied by a UGF and a handful of leaf litter (I have a set of AZOO pipes if you want them), your PH will drop to about 6 - 6.5 which is perfect for CBS/CRS. Keep the TDS around 150-200 using NACC mixed with your pure RO and do 20% WC every other week. That's it! Later as the tank gets more mature, you just top off regularly with RO (no remineralizer), and do less and less water changes. Maybe once a month if you feel like it. Simple as that.