Q: I water by immersion of the entire pot into water containing weak fertilizer. Can I add a bactericide like Physan 20 to the regular watering? If so, at what concentration?
A: I have been doing exactly like what you describe for a couple of years. It is to prevent mold and algae growth inside the pots. I haven’t seen any issue/negative effect so far. However, it is just my personal experience (I have no scientific proof).