Hi mate,
If you want to do things right and achieve the best results, you should change out your nute mixture every week. Wait a couple weeks after you introduce the plants into the system before you change it out the first time.
You should check the pH level every day, that is the most important factor in hydro. It needs to be between 5.2 and 6.3, and shouldn't vary more than 0.5 in 12 hours- you don't want to shock your plants with a quick change. Also, if you don't have a ppm meter your pH can help you determine how much nutes to use (your babies are ready for a low concentration nute mixture when the second node appears). If the pH is rising, your plants are using up nutes and you should add a higher concentration. If the pH is dropping, your plant is using more water than nutes and you should add a lower concentration or just water.
So all in all, it’s the plants that will tell you what you need. Although being in hydro,when things go wrong it’s already too late. So take your time and regular checks on your girls. Slow and steady wins the cultivation process. All just advice at the end of the day, free to do as you wish. Just giving you some knowledge from my past experiences.
Hope this helps. FlavoursUk 👌