PH IN DWC fluctuation

No need to be so precise, unless you are OCD, pH in that range is fine. As long as the pH doesn't go below 5.5 or over 7.5, nutrient availability won't be affected greatly. The correct way to check pH is after 24 hours have passed and the solution has stabilized. Testing immediately after adding any sort of pH up or pH down will give a "false" reading due to the fact that the solution/nutrient mix has not had a chance to fully "acclimatize" and for all chemical reactions to finalize. The first reading will give you an indication, but the reading taken after 24 hours or more will be the true reading. Hope this helps,........ Organoman.

It's very hard though its possible. I try and change my water every week without fail and I dont seem to have many problems with Ph fluctuations though as a grower has said it can be used to your advantage towards the end of a grow though I tend only not to ph to 5.8 if im flushing and thats the only time I aim for 5.8 and the reason it is aimed at 5.8 i can only assume is to have a large buffer zone for 5.5 to 6.5 and having that slap dab in the middle no matter the fluctuation if you are changing your water weekly it should never go higher or lower than that range. That is just a guess but that would make sense in my head anyway. I aim for 5.8 though usually when Im testing run off it comes out much higher 6.0-6.2 sometimes it can be lower though it is very rarely 5.8 when I come to change the water.

Hydroponic setups are likely to see pH levels rise over time, as the system becomes more alkaline. Why? Most nutrients are slightly acidic. As the plants absorb these nutrients through their root systems, the system slowly loses its acidity to become alkaline. Over time, the pH numbers will gradually rise until you add more nutrients. Temperature also affects the pH level of water. As the water warms up, it slowly releases CO2 into the atmosphere, which naturally increases pH levels. The strength of your nutrient solution could also affect pH drift. If the solution is too weak, pH is likely to rapidly rise as the plants absorb the available nutrients out of the solution. On the flip side, if the solution is too rich, you'll see the pH head towards 0.