Wow....those look like some sick plants. Somehow they are burning. I don't really understand the rain water and UV filter so I'd start to wonder about your water first off. What's the ec of it? Rain water really isn't as clean as some people like to think and I'm not sure about the bacterial thing so I can't comment on that. id also wonder about enough calcium and magnesium from rain water but again, am not sure.

Until you figure out what's going on I'd stop ALL nutes and I'd go back and recheck and recalibrate your ph meter (or at least check and make sure it's calibrated correctly)
I would put them on ph correct water until you can pinpoint the problem. Rockwool is known for it's ph issues. Maybe the ph of yours is abnormal.

From the pics you've provided it honestly looks like everything is wrong. They look overnuted and nuteburned AND they look like your ph is off. That brings me back to wondering about your water. Have you used it before with success?

Hope you figure it out.

Good luck.