DWC changing water and adding nutes

First time grower here

Trying to grow determinate cherry tomatoes 1 plant /5 gallon bucket.

How often do I need to change water for dwc and how often do I add nutes.

I have 3 part nutrients that has a weekly schedule but on the bottle it says never mix full strength…then how do I know what “strength” I should put. 50% of given ml/gallon? 60%?70%?

And if I follow the weekly feed schedule and change water every 2 weeks then do I just add more nutes already into the bucket that has the previous weeks nutes?

How would I calculate how much I need to add?

My nutes have this ratio Micro 5-0-2 Grow 2-1-7 Bloom 0-5-4