You are lucky to have Physan available. Physan 20 is I think the version designed for higher temperature areas (the tropics) and ordinary Physan for temperate zone areas. It is great for plant hygiene, which means cleaner stronger healthier plants.
Unfortunately it is no longer sold here in UK ( it is not "licensed" and doing all the work to get a licence would cost , so I am told US$400,000...due to bureacracy - which gets me steamed up....) and the cost of a trip to New York, for however many gallons I could get in my luggage to bring home is just not on - but I did consider it !
I used it from about 1990 onwards, until the supply stopped last year. I always added some to the water used for my orchids or for spraying ,at the rate of anything from 1:5000 ( in water/nutrient mix) down to about1:1000 which is approx 1 teaspoon in 1 gallon for spraying all the foliage once a month . It is a fungicide, insecticide, miticide, etc - or in other words a disinfectant which most pests will dislike, so that they don't hang around and don't spread. It is also a very good wetting agent , which means that the water really spreads around and there are no dry corners.
This practice - the monthly spray - started when I visited and was told that this is what they do at the Eric Young Foundation which has one of the best grown orchid collections in the world. What's good enough for them, will do for me.
Nowadays I use another similar product which is licensed in UK - one actually intended for sterilising surfaces used for food preparation - almost identical chemical formulation, and a lot cheaper per gallon ( Selgiene) but I have to use it a bit stronger down to 1:500.
Go for Physan !