Hi thelastbetta,
Here's some of what I know and deduce about ich. Ich is a parasite that exists in all water. It has several life stages so it is near impossible to completely rid a tank of the parasite. It can also go dormant until there is an opportunity like a fish with a weakened immune system. Every time you do a water change new parasites are introduced into the tank with the new water. There is no effective treatment for some stages of the cycle. The good news is that a healthy well cared for fish is not susceptible to an ich parasite. But when a fish is weakened and infected the parasite becomes more virulent and mutiplies. The increased parasite activity and attack will then begin to weaken other fish and the parasite spreads and continues to get more virulent. Often wiping out a whole tank.
The other good news: The parasite needs fish to live. If it is in a tank but no fish are in the tank, it will die--or at least go dormant. Your plants will not sustaon the parasite. In addition the parasite dies at high temps. Its life cycle is about three weeks. Change the water. Increase the tank temp to about 85 degrees Faranhiet for three weeks. No fish or animal in the tank. Your plant and tank should be safe. Clean the tank well. If you want the academics and scientific names of all the stages,etc., there are forums with pinned ich threads. I'm willing to warranty that RandomWiktor can also give you a very detailed and "correct" explanation.
By the way, sorry about your girl.
