Hello; the Rid-ich sound like it may have methylene blue dye in it. Methylene blue has been around for a long time. If so, there are some issues with it.
It did seem to work on some problems like ick and some fungus problems. It is a staining dye (used in microbiology to stain slides) and will permanently color some things in a tank and around the house. Not the glass, but clear silicone, plastic tubing and several things can and have been stained light blue in my use of it. It also stains fingers and sticks around for days until the skin layer comes off.
I think it also is absorbed by organic material in a tank such as plants, tank debris and filter carbon. This absorption means having to add more of the blue dye. I recall removing plants, which is a pain in a well planted tank. This was one reason I started keeping a QT for new fish without any rooted plants. In a bare tank these issues are not a problem and the new fish are treated before going into a main community tank.
A successful fish shop used to keep small plastic containers hanging on the outside of each tank with a solution of the methylene blue in them. They would keep the nets used to catch fish in the solution as a way to avoid spreading parasites and disease from tank to tank. They also had one or two nets for each tank and were mostly careful to use them in only that tank.
On that note, They would take water from the tank that held the fish you were buying. If you bought fish from a different tank, they would use a different bag, net and use water from that tank. I would sometimes have several bags from one shopping trip. I do not see that today in fish shops. It seems that good ideas do not always endure.
