I started with 6 cardinals and down to three now. I lost one due to screwing around with the GH and then 2 more when my heater sensor left the water and cranked the temperature up to 90! =
At $13 a shrimp those were some costly losses. I would house cardinals completely separate from your CRS. Those two in no way belong together in the same waters. I suggest getting a substrate that will buffer your water a bit. Although I have heard of folks having success with CRS at that PH as long as the water is stable and clean they should be fine.
If you have the funds I would invest in some aqua soil amazonia though.
I've had mixed feedback on OEBT. They do not breed true and can be a bit finicky. Your offspring can range from regular tigers to really dark tigers. They never come out as nice as the parents.
I almost got some too until someone told me about their experience with them. So I've decided to go the taiwan route and have 10 coming. =)
The shrimp list so far now is:
A couple of left over ghost feeders
and BKK and WRs on the way.
Its a bad addiction.