If your test results are in ranges recommended in pool school it would indicate to me that you have some particulates, either from construction or just normal wind or dirt from people in and out. 10 psi drop on your sand filter is pretty large! Indicates you are trapping something and probably what is causing the cloudiness in your pool. It also indicates whatever is clouding the pool is getting removed effectively with your filter as is so I wouldn't be in a hurry to modify it. Just back flush it completely and perhaps a couple of times per week to see if that clears up the pool. Use the dime test to measure progress.
How long did it take to get this high? Back flush intervals can vary depending on usage, weather, dust etc but once per week is common. Watch that pressure, when it gets high water flow through the filter is reduced making your problem worse.
I just backwashed 3 days ago and a lot of dirt came out, but I'm still having the murky issue. I'm trying to avoid having to pay another $350 for another water refill so I'd rather not backwash unnecessarily if I can avoid it. This is the first time I've ever backwashed it. Here's what Pentair says about backwashing my filters:
Cleaning Frequency
1. The filter on a new pool should be backwashed, and cleaned after approximately 48 hours of operation to clean out plaster dust and/or construction debris.
2. There are three different ways to identify when the filter needs backwashing.
a. The most accurate indicator on pool systems with a flow meter is to backwash when the flow decreases 30% from the original (clean filter) flow. For example, if the original flow was 60 GPM, the filter shouldbe backwashed when the flow is reduced by about 20 GPM (or 30%) to 40 GPM.
b. A more subjective and less accurate indicator is to observe the amount of water flowing from the flowdirectionals located in the wall of the pool. The filter should be backwashed once it is detected that theflow has been reduced by about 30%.
c. The most commonly used but less accurate indicator is to backwash when the filter gauge readingincreases 10 PSI over the initial (clean filter) reading.
3. It is important not to backwash the filter solely on a timed basis such as every three days. It is also importantto note that backwashing too frequently actually causes poor filtration. Factors like weather conditions, heavyrains, dust or pollen, and water temperature all affect the frequency of backwash. As you use your pool, youwill become aware of these influences.
4. If at any time the starting pressure after backwashing the filter indicates 4 to 6 PSI higher than normal startingpressure, it is time to perform a chemical cleaning procedure.
