Your few hours of sunlight explains some of what is going on -- namely that your chlorine usage is probably low. If I figure that it is only 1 ppm FC per day, then in one day the pH would only drop from 7.2 to 7.15 so not be noticeable and that assumes no carbon dioxide outgassing. If you are going to be gone for a week so we figure 7 ppm FC, then the Trichlor will lower the TA by around 5 ppm so I would just raise your TA by 10 ppm to 60 ppm and your pH to 7.7 before you leave. That will have the pH drop to no lower than 7.2 after a week, assuming the 1 ppm FC per day assumption is correct. That seems reasonable. You don't have to raise your TA way up because you'll probably be frustrated lowering it again for pH stability when you return (I assume you have the TA very low for pH stability when using bleach or chlorinating liquid -- if not, then raising it to 80 ppm would be OK).