Dropping SG fast is just as much of a shock to the livestock as it is to increase it. That holds true for any parameter that we test, and ones we don't test. Corals tend to do well in higher SG levels than lower. Drop your SG from 1.028 to 1.022 in one sitting and see how the corals will react. Moderate changes like this should be spread out over a week or so, not all at once.