No... As the rez gets lower, your ppm's usually go up... adding more nutes to the water you use to top your rez will give you more ppms and you could end up burning them more....
I would just top with pure water... check the ph of the rez after topping off and set it and next time it needs more water..... dump it all out and start all over..
So you will.....
-do a complete rez change with new nutes
-when water goes down, add just water
-when water goes down again, do a complete rez change all over again.
This should keep you stable until you get a ppm meter and can better control what is happening in your rez.