Typical for me for the first 2 days, so I PH to 5.5 in the AM then check it in afternoon usually up to 6.2-6.3 by then and then put it back down to 5.5, Check it once more the next morning and usually it holds around 5.8 - 6.3 which is in all honesty a good fluctuation but yes the best point to keep it at is 5.8
If your not running nutrients the PH will always rise because there is nothing in the water to buffer it