In a case like this, where the plant is still alive but you might want to clean the reservoir, we have to take the whole lid and put it onto a bowl or pan or bucket. You could put a little bit of h2o2 + water in the bucket to help clean off the roots too. Kind of like a temporary reservoir while the cleaning occurs.
It’s a pain to stop and clean while it’s still alive, I would only usually recommend it if it’s really bad (like a white mucus-like goo on things) or if things don’t improve just with treatment. You’ll need to unplug the bottles and take the ph/ec sensors out (and keep them hydrated in the meantime). How do I clean my Grobo?
For the past 3-4 grows I have managed to get away with “bombing” the reservoir with a product such as you’re using and then giving it a week or two to clear it up. It’s much easier than a deep clean (if it works)!