To reduce ich ,try :
1. Uv steriliser
2. Medicated fish food like Dr G 's parasitic or new life spectrum ich
3. Drop salinity to 1.021-1.022
4. Shorten the period for lights to give the fishes enough rest
5. If fishes are eating as per normal, just leave them and not to stress them
6. Use ozone
7. Reduce strength of wave maker
8. Frequent water change ?
Usually I will use these methods for newly added fish