I understand about the gas exchange this is why I keep ventilated tops. So from smoking inside my room I now shouldn't be doing water changes? Ahahaha. Oil sticks to surfaces, its the same when you put a lot of treatments in the water, its easily fixed and poisoning fish? That actually what I wanted to hear, if you could go into detail about this that would be great. The reason I no longer smoke heavily in my room is for this exact reason. I just thought I would post what happened to me, god with the way your posting my trimacs will be swimming round with nic patches on them next! I am posting because I would rather my fish do not get poisoned lol anything else?