Why does my ph keep rising?

Latest readings:
tc 2.5
fc 2.5
cc 0
cya 40
alk 150
ph 7.8

intex above ground 18x48

Yesterday all readings were the same except ph was 7.5

It took us a long time adding muractic acid and then aerating to get the alk down, but now the ph keeps rising. We will add acid and it will drop to 7.2 to 7.5, but a couple of days later it will be up to 8. What do I need to do?