I forgot are you growing Hydro or dirt.

Hydro flush Only use Ph adjusted RO water.
Day 1 - you change the res add florakleen per the directions.
Day 2 - Do a full change of the water & florakleen again. Record the PPM level this time.
Day 3 - Check the PPM and see what the change is from day 2. If there is more then 25 PPM change goto step two again.
Day 4 - See day 3. Once the PPM only changes 25 PPM or less for 24 hours you are done.

Dirt you can follow the same steps but you need to catch the water runoff and are looking for only about 100 max change or less.