First things first.Relax and smoke a bowl.
I'd recommend getting a cheap dropper ph kit as a back up.
5 bucks at wallyworld.
Personally, that's all I use. But that's a different thread...
This is where keeping notes comes in handy.
For example, for me, my H2o is @ph 8. When I mix up my current nute blend ph is @ 8 still. I know for my 2 gallon res it takes me 1.5ml ph down to get it exactly where I need it.
I usually do all the mixing and then test ph. This has remained consistent every time I test it.
Knowing this, If I didn't have my tester, I would at the minimum, know what my ph is at on a new res change.
If you are consistent in what your doing you should be able to run blind for a day.
I know of some folks that taste their res and know when it's good or not. (not recommended!)
Just saying.. everyone has their own method of madness on how they run their set up.
You should be alright if it's just a day. Just keep an eye on things.
Canoed leaves?
Can you throw up some pics?