The wording of the first post is a little confusing. So, I will just sort of start from scratch. With loaches in the tank, you do want to decrease the dosage, half is a good place to start. If the ich is persistent, increasing the dosage may become necessary.
However, you have to dose every single day. Ich is only vulnerable for a short time frame, so there has to be medicine in the tank ready to attack ich over the short time frame. And the time frame is short, only a matter of hours. Outside of this short window, the ich protects itself and cannot be killed. That is why you have to add medicine every day until 3-5 days after all signs of the parasite are gone. I even usually recommend 7-10 days until after the parasite is gone, to make sure you go through 2 full life cycles of ich. If you didn't know, ich's life cycle is about 3-4 days at tropical temperatures. Simply put, that means that the ich is vulnerable every 3 days. But, if you only dose every other day, some portions of the population will miss the dosings. Your fish may even start showing relief, you may not be able to find a single whitespot, but a tiny portion of the ich population may exist, and it will only be a matter of time before ich comes back. So you need to add medicine every day -- you have to have medicine in there to catch every ich as soon as it becomes vulnerable.
Please reach through this page about ich:
http
/www.skepticalaquarist.com/docs/health/ich.shtml The best thing you can do is know thy enemy. This has a lot of great information about what is known about ich, what isn't known, and discussed a lot of the ich myths that are rampant on the Internet.
As to the water changes, I would do as many water changes as possible, immediately before adding medicine. Most medicines work by oxidizing organic material. Anything organic -- this includes plants, fish tissues, old uneaten food, fish waste, etc. So, what you want to do is remove as much organic material that the medicine will oxidize and therefore be unavailable to kill the ich. So, a good thorough tank cleaning with a water change BEFORE adding medication is a very good idea. Because the ich medicine is so reactive, in about a day or so it loses a great deal of its effectiveness. This is another reason why you have to add new medication every single day.
So, in recap. Medicate every day, even if it is only a half dose every day. A good tank cleaning with a water change is a good idea immediately BEFORE adding medicine, as well.
Good luck in your fight.
