Doing this type of testing will definitely save time and fish lives however, as it stated in the article ( or posts after the article) this is for bacterial issues only. So this will only work if you know what the issue is or you know it's bacterial.
There is a good book on fish diseases that I highly recommend everybody gets as the first step.
Handbook of Fish Diseases by Dieter Utergasser has one of the best diagnosing chart system for the beginner to advanced hobbyist. It uses an " If this, do that or go there approach." It's an older TFH distributed book ( Don't let that fool you) which when I just looked it up on Amazon, seems to be having a revival on the higher price. ( I guess enough people took the suggestion and started buying them up.
) I saw used from $5.55 up to $35.00 for new. ( I paid about $3.00 for my used copy a few years ago.)
Here's the thing with the book: you are not buying for the pictures or medications it suggests. You are buying it for the diagnostic charts so I suggest not investing a lot of money into the book. The disease's symptoms don't change all that much over time so what it looked like in 1989 is what it will pretty much look like in 2017. As long as the charts are in good shape, you should be good to go.
Once you know
WHAT you are treating, you stand a much higher chance of actually curing your fish. You can then use the method of sensitivity culturing if it's bacterial and external or if it is something else or internal, contact your local LFS or internet supply house for what they have available to treat that condition.
Proper diagnosis is the key to curing your fish!!!
Hope this helps.