Should I top off res during flower?

One of the girls is drinking so much 3 weeks into flower. Should I top off the res with ph water? It's more than half empty 3 days after a change and I'm changing res every week.

better to top off than run out

Of course, you should refill. I try to maintain a consistent ppm reading, that will show you if you need to alter the amount you're feeding your plants.

This is knowledge I didn't immediately see in any of the guides or that I wasn't able to clearly extract. Thanks for painting the picture! Important stuff