Hi new to this forum. Completed a PH level increase- think it was too sudden an increase and have stressed out fish (they are crashing and diving all over the place). Its late at night here (Sydney Aust)-so no local advise available. Please, what can I do to rectify the situation?? Thanks for any suggestions! Pete

A water change should provide a temporary fix until you figure out what is causing it.

What has your ph been previously and what is it now? Have you added anything to the tank recently? Rocks? New gravel? How long has this fish tank been up and running? Have you tested ammonia and nitrates to rule that out as a factor contributing to your recent fish deaths?