Hard to say if that's the cause, but I know my LPS are much more sensitive to an alk swing than they are to any particular steady level (within reason of course... Stability at 5 or 13 would obviously be bad)That was an early struggle and I was wondering if the Marco Rock leached it instead of absorbing. I use IO reef crystals and typically in the old system it would bump it to 10. I supplemented with All for Reef to keep it stable around 9.5. When I filled the new setup it was 11.4 from the start and have been trying to walk it back from there. Do you think that Alk is doing it?