I have used Kick Ich which is 5-nitroimidoles, think it is a relative of flagyl. I have had ich twice in the 5 years since having saltwater fish and it has worked both times. Was ich free for two years and recently introduced a new fish and exactly two weeks later this fish has ich. The other fish in the tank did not show any ich except for one fish had a couple of ich spots on it's tail. It could be since they had had it two years earlier that they had some immunity to it. So, this is actually my third time to use the Kick Ick. Started dosing the Kick three days ago and don't see any more spots. I will continue to dose the Kick for a total of 5 to 6 weeks straight as I know that in the past if you stop dosing after only two to three weeks, even though the spots are not visable, it will come back in a couple of days. When I dose for 6 weeks without stop it has stayed away for two years. The stuff did not kill my shrimp or crabs or affect my biofiltration. All the moderaters on this site will tell you it does not work but it does for me. It may be too late for you if you don't catch it when it first comes the fish can be too weak to recover.
Here is how the bottle says to dose....beginning on day one add 2 oz. per 25 gallons of total water volume including sumps etc. repeat dose on days 4, 7, 10 and 13. It says that you may repeat the cycle. It says for heavy infestations to repeat instead on days 3, 5, 7, 10, and 13.
Here is what Lesley the RN does successfully. I dose 2 oz. of Kick per 25 gallons on day one, then dose 1 oz. per 25 gallons every single day for 6 weeks straight. I do 25 percent water changes weekly while doing this as you must turn your skimmer off, remove any carbon type media and turn off any UV filter if used as all degrade the medicine. Since it only kills the swimming stage I dose in the morning because I have read that the swimmers always hatch in the morning and it is a good time for the med to be the strongest at this time to kill the most of them. I dose the smaller daily dose as any medication degrades some if it is in the water with the rocks and lights etc. for any length of time and becomes less effective. Daily dosing keeps fresh medication in the tank where it can kill the swimmers better. I do this for 6 weeks straight as I said, even thought the spots are gone in a couple of days they will come right back if one stops in only 2 or 3 weeks as some of these buggers are tough and since Kick is a weak, but reef safe killer some might still survive through the first two week life cycle but it gets to the point where fewer and fewer survive each life cycle until they are gone. Sure beats taking all the fish out of the tank. I dose like this as I know from real life with bacterial infections my patients often go home for at least 6 weeks of IV antibiotics which even continue after the infection looks gone after a few weeks as there are always stragglers that are tougher and will come back and multiply if the med stops. I know that ich is not a bacteria, but the principal is the same. Says it is safe for corals too...don't really know but it has not killed the mushroom corals and my brain coral which are the only ones that I have. If one can get a fish out of the tank that is heavily infested they can benefit from a 2 to 5 minute dip in fresh water of the same temp which is ph adjusted with about a half a teaspoon of baking soda per gallon to match the ph. If the fish seems stressed take him out sooner and place him back in the tank. Did this with my new wrasse this time which started to act funny after two minutes. Put him back in the tank and he was fine and the spots were all gone by the next morning as the osmolarity of the fresh (dechlorinated) fresh water makes the spots pop which is only aparent after a few hours after the fish is put back in the tank. The Kick is about 40 dollars for a large bottle at most fish stores but subsequent bottles can be purchased on line for about $23 if you have a large tank and need a large amount like I do it is worth the shipping fee. Got to buy the first bottle locally or the fish will die waiting for you to get it. Good luck, Lesley