Simmer Issue

We just opened our in ground 27000 gal saltwater pool. We changed out the filter sand and put 300 pounds of new sand in. We have been using the main drain to clean the pool. We just today put in enough water to use the skimmers. At first we couldn't get the skimmers to work at all. I tried using the re-circulation setting on the filter and it worked fine. I then switched back to skimmers and they were working ok. However after 20 to 30 minutes the skimmers stop and I have to switch back to re-circulation for a few minutes and then back to skimmers. The pump is working fine so I am not sure whats going on.