Kordon has been in the hobby for over half a century, and they have things pretty nailed down when it comes to medications.
Ich Attack and Rid Fungus are both 100% natural products. They are equally effective in both fresh and saltwater and are reef and invert safe. For more information on these products you can click the link for them.
Rivers to Reef says: These natural medications, while effective, are pretty gentle. They can take quite some time to work effectively since they are less harsh. Treatments for these products run in the weeks, so stick to it and eventually your problem will be resolved. It's nice that both of these are reef and invert safe so you can treat fish disease in those respective tanks with little worry.
Rid-Ich is a blend of formalin and malachite green that is very effective against Ich and many other external parasites. This product is NOT reef or invert safe, so a quarantine tank would be required if you wanted to use this product. Please see their site for more details.
Note: This will stain the silicone on your tank and any air line you have.
Rivers to Reef says: We encounter Ich way more than we would like and this is our go to medication for it. It very often treats the Ich quickly, which is great for you and the fish. Follow the instruction carefully as you wouldn't want to overdose your tank. After it appears the Ich is gone we recommend running one more treatment cycle, just to make sure you take care of any free swimming Ich.
Methylene Blue can be used on fish as a fungal treatment, but primarily it is used to keep fungus off of fish eggs. For more information please visit their site by clicking the link.
Rivers to Reef says: If we are pulling eggs we always dose with methylene blue as it prevents healthy eggs from growing fungus. Gentle water flow across the eggs and removal of unfertilized eggs is also essential in raising a full clutch of eggs.