Most of the ich medications on the market do work. The bottom line is how well are directions followed, the main chemical ingredient, the type of fish being treated and how long treatment with that medication is.
Parasites, just like bacteria and viruses can become sort of immune to medications made to annihalate them. It's a natural evolutionary adaptation to the outer environment. There is also a stage of ich that is difficult if not impossible to kill with medications. Larvae of these critters are well protected and may even emerge with a level of tolerance. That's one reason why ich meds don't 'seem' to work. Best to use a medication for two weeks if needed, but if further treatment is needed, use a different medication with a different chemical ingredient.
Many times we see ich on fish and go right out to treat it without checking up on the water's condition. Testing for nitrates is important. The more saturated the system is, the more likely of a difficult to get rid of colony due to an explosive population boost of ich in a nitrate saturated system. Dumping chemicals in there might rid most, but that's when repopulations can possibly develop a good strong tolerance of the chemicals. Best thing to do in such a case is to tend to lowering nitrate levels first and just use simple first aid to hold the fish over till further treatment can be administered if needed....such as...melafix and garlic additives; freshwater dips for most saltwater fish and brackish dips for freshwater fish. Once nitrates are lowered to under 40 ppm
, then the medications may have a chance to work. Otherwise, it's nearly a waste of money using any brand of ich treatment.
Another important thing is to remove carbon materials from the filter when medicating. Carbon will absorb the medication.
Chem-Marin products should work just fine if directions are carefully followed and the system isn't nitrate saturated.
We, as a people, know so much more about outer space than we do about our own oceans. This lack of knowledge can very well spell the dangers that lay in wait for us.
The oceans surely would swallow us before a rock comes down to smite the planet of it's life.