You should be fine. That is if your PH has only been low for a while....It takes quite a few days for ph issues to really take hold and fuck up your plants. I know, low batteries in my PH pen caused me to kill a God Bud plant 3 weeks from harvest. Took about 5 days till I realized the problem by than the damage was done. If you make a trip to the hydro store your top priority tomorrow, you should be fine. If you tap water is higher in PH, add some extra straight tap water to your rez......