help DWC PH issues

i have a 24 litres res with about 9 litres of water in it , i have 4 plants in it that are only like 5 inches tall , every 4-7 days i clean out the res and put new water in at the ph of 5.0-5.5 and every time i come back to change the water its at about 7-8 ph ... now is this normal ? should i be adding ph down everyday to keep the ph in check ? is there anyone out there that just sets their ph once and thats it lol ?

i understand plant activity increase ph levels whilst the light are on but from 5.0-5.5 to like 7-8 is a big leap

that is strange since nutrients usually lower the ph.. are you sure your nutes aren't bleaching your water a certain color? If not, guess your gonna have yo regulate it every few days.

my water colour is normal and yes u are rite adding nutes does drop my ph ... it dropped it to around 5.5 but my questions is basically is this normal for ph to rise like that within like 5 days ? and if it is everyone would just be stressing there plants everytime the change the water ph down that much.

shit i ph my water everyday... but i also have to add water everyday