Thanks you both! Im giving the answer to Grey since last time you both answered I gave to Mrs Larimar. Im still new in here so IDK if you win something by that, so...
Anyway it may be Ph Fluctuation because I'm not using a PH down for now because I dont have one yet. Ordered it and it should come by monday.
Or actually maybe I have just spilled a bit of nutrient solution as well 😅