So I'm going to test and troubleshoot the probe.

Blenny has died .

So I have multiple things to work out...

- fix PH probe
- get tank back to an acceptable PH level
- determine why PH is dropping


So it seems to be obvious that the blenny died from the PH drop; however, it could just be a coincidence. Beemer, the tailspot blenny, and the pipefish are acting totally normal. All inverts and copepods are in good shape, and the corals look normal for my tank. It could be that the sailfin was just super sensitive. But what if it's something else?