I have an in ground 22,000 gallon salt water pool. Took my water sample to local pool store and started to balance everything. I have added shock, DE, and salt so far. After DE was added pool filter was running fine (even with Polaris running). PSI started around 15. After about 4-6 hrs of running my PSI jumped to 20 then 23 and I shut the filter off, back washed and re applied DE. Turn the filter back on and the PSI goes directly to 20. Is this safe? The PSI jumps so fast it sounds like the filter is actually makes a "cracking" type noise momentarily. Any ideas what the problem could be or suggestions?