It is possible for sharks to get ick, BUT assure it is not sand that does stick to their bodies temporarily. If ich, you can treat by dropping the salinity range to 1.018 for 5-10 days although this can weaken or kill them as they are semi-isotonic and will not thrive or probably live long in conditions under about 30ppt. You should really keep the salinity for sharks around 36ppt. If you must treat them chemically. then treat with formalin bath @ 150ppm for 10-15 min with great care or it too can kill sharks AND do not treat with copper. Only use copper with wobbegonges nurse sharks and epaulette sharks at low concentration.
Hyposalinity - NO good whatsoever IMO. I recommend Quick Cure as a means of formalin