the supplements you should use are:
calcium-helps build skeleton
strontium-helps build skeleton
magnesium-helps prevent premature calcium precipitation
iodine-helps prevent damage due to excessive light exposure
buffer(alkalinity)-helps build skeleton, buffers ph.
trace element-helps facilitate enzymatic and photosythetic reactions
plankton suspension-provides nutrients that are not produced by the target organism.
vitamin-helps maintain health, color, and facilitates biological reactions
Not to be "contrary" here, but just to offer my opinion/experience.
Calcium & alk
should be maintained with a reputable 2-part additive - be it kalk
, B-Ionic, or a calcium reactor.
Strontium & Iodine - many recent discussions indicate that adding these as 'supplemental additives' does more harm than good.
Magnesium & general "trace elements" should be maintained with water changes.
Bottom line - add no supplements/additives that are not confirmed as deficient by a reputable /accurate test kit.
Plankton suspension/vitamins should be added very sparingly, and IMO
, should be incorporated into a good feeding regimen - if possible, as part of a homemade food mix.
As far as the leathers go, I agree with Steve. These corals are notorious for regularly 'shedding'. They also don't like any detritus accumulating on them at all - you might try gently blowing it off with a turkey baster to see if any of the sand settled on it.