Ph questions

Ph I have a 4) 5gl rdwc setup My issue is when I set my ph to 5.8 with in 24hrs the ph will jump to 7 plus I seen it hit 8 before But over the next few days it will naturally drop back down is this normal or should should I be trying to adjust it back down to 5.8 or let it ride I haven't been chasing it just letting it go till it drops below 5 then I change the water
Ps the plants looks great even tho the ph is jumping around Sorry about the grammer