Below is a more advanced method to tops ups.
Generally an EI (estimated Index) type system has been traditionally used in hydro. This was taken from the aquarium hobby but only partially.
So as nutrients are taken up they are not taken up in the exact ratio that we supply them in. This means over time our nutrient ratios change and this the need for a complete res change.
Some do weekly some biweekly etc etc etc.
To keep ratios withing a certain range.
By topping up WITH nutrients you can delay this indefinitely.
But you can also make the most of the nutrients by combining it with water changes.
How i do it is to too up using the method below. Then doing a complete water change once i have added back the actual water volume the system holds.
I can explain more if you like just for understanding purposes but understand there are many ways to do this successfully. I just feel this way keeps nutrient ratios very stable and leads to the reduced amount of water changes then the traditional once a week.
In the early stages you may only need a water change after over a month or longer. N the late stages where they drink a lot you may need it weekly.
The general concept come from as i said Estimated Index for aquariums so you can google that to get a bit more context. Generally for planted tank nutrients but also for water quality maintenance of nitrates to keep safe levels for fish
Thread 'RDWC advanced top up method explained by Aqua Man'
https://budbuilders.org/threads/rdwc-advanced-top-up-method-explained-by-aqua-man.209/