1 more method u can try that work for me , i had ich on my tangs a couple of weeks back but after using this method for 1 week , i had not seen anymore ich on my fishes , still monitoring
go to hardware store to get a tapwater filter ($38) get 1 that uses a 5 micron filter, hook it up to a powerhead of at least 2000l per hour place inside ur tank and polish the water, when the ich breaks offs from ur fishes they will be free floating as well as baby ich will also be in the water colum before they find a host to attach to, their size will be arn 30micron , so the filter will definately filter them out , filter must be taken out and flush with hot freshwater for 10mins daily, feed multiple small meals to make sure ur fishes are eating. for tangs put in dried seaweed and red bamboo algae, do a weekly water change.
troublesome but it seems to work for me , and also a big warning to me to quarantine all fishes before adding to display tank, the ich was brought in by a blue tang which was stress.
oh ya increase the current and stir the sand then while using the filter to do the filtering do at least a 20% water change , u might have to change the sucking position of the powerhead daily, in 2 days u should see extremely clear water with good light penetration and the fishes should look happier and corals opening bigger
u can try this method hopefully it works for u as it did for me, try not to put any medication into ur tank if it has corals that you cant take out
but a word of water , its a very tedious method, took me a whole day to do everything excluding flushing filter daily but mine is a 5x2.5x2 , so urs should be much easier