5 gallon Fluval Spec V

Some more images of the tank and shrimp - they’re doing really well and I’ve seen a couple more molts so far which is a great sign

Somehow two shrimp have died, one a berried female. As of now I have 5 shrimp remaining, 1 a berried female. I'm not sure what happened but my brother believes it was a molting failure for one, but the female he is unsure. I tested parameters and found GH 4 and KH 2, which are too low and too high respectively. I did a 50% water change with remineralized RO and I'll keep checking in on the shrimps. In the meanwhile does anybody have any ideas? So far they looked good and I didn't see any parasites. On the female there were some rusty spots but I don't think it's rust disease. Hopefully it isn't and it was random, but I am worried.

Thanks