How long have you had the bicolor and the other fish in the tank? Is the bicolor the only fish with ich so far? Is the bicolor a new fish? Seven fish that size in a 25 must put a big bioload on the tank. How often do you have to change water? If the bicolor is new, the ich could be caused by stress. I'm pretty sure that's what happened to my tang. He got it the first few days he was in my tank. I started the Ich Attack treatment the next day. Like I said, I never saw one spot on my puffer or chromis. If no other fish is exhibiting ich, you could put the bicolor in a 10 gallon as suggested and start treating him. Do the hypo treatment on him alone. Of course the ich experts will say you have to treat your DT, because once ich is present, you have to go 'fishless' in the DT for SIX weeks.
I've talked to several individuals who have been in this hobby for 10 to 20 years, and every one of them say ich is always present in a tank (I'm sure that will start another debate). If you keep your fish healthy and stress-free, it's unlikely they'll ever have an ich breakout.
You just need to decide what's best for your situation. I have read the posts here of people who got ich on one of their fish, and in a few days, all their fish had it. Many lost every fish they had to ich because they didn't treat it fast enough. The big debate is how to effectively treat each case of ich. Yes, hypo is the defacto method that has shown the most success. But is it absolutely necessary in every case of ich? As in my case, no. I had one fish get it (Mr. Tang the Ich Magnet), and decided to try the alternative methods. For me, it worked just fine. That may not be true for you. Again, you have to access how bad the ich is, and whether it's spreading to your other fish. Treat apprpriately.
Just remember, if you decide to go the QT route, you also have to deal with cycling this new tank. You can't just fill it up with water, put a heater in it, and move your 7 fish into it. Like any other new tank, it has to go through the cycling process. You can try seeding it with bacteria from your DT (a used filter out of your main pump, if you have one), but you will have to deal with the nitrate and ammonia spikes. Don't monitor the levels closely, and that alone can kill all your fish. Also be prepared do do ALOT of water changes. You think you have a bioload problem in your 25, wait until you put the same amount of fish into a tank less than half the size. And you have to do all these water changes while maintaing a perfect 1.009 salinity level for three weeks. Oh yeah, rememeber you have to fork out at least another $40 for a refractometer to accurately monitor your SG levels while in hypo. That plastic hydrometer won't cut it. Isn't QT and hypo fun!!!