I use the same treatment, but one thing I need to point out is that when instructions say “day four†it means 3 days later not 4 the 1st treatment is day one (it is important as it is relevant to the life cycle of the bacteria being treated). It’s all about knowing your enemy. So here goes…
Ichthyophthirius multifilis is the protozoa that causes ich or white spot has a life cycle of 12-16 days. It shows as white cysts on the fish's body and fins. These cysts are called trophonts and they drop off the fish releasing tomites (free swimming stage) into the water. These tomites then attach to a host, mature into trophozoites and bury themselves into the skin of the fish and become trophonts.
This is important because it affects the treatment, the tomite stage is the ONLY stage affected by the treatment and only lasts 3 days hence treating 3 days apart not 4. You also need to treat every 3 days for the full life cycle (not just the 2 times it says on the bottle). This is because the adults won’t be affected and nor will any cysts, so that’s days 1, 4, 7,10, 13, and 16. Each treatment needs to be preceded by 50% water change as you don’t want to overdose your fish. The tomites also do not like higher temperatures so raise the tank temperature to up 18-30C and siphon the gravel regularly to remove some of the trophonts from the bottom.
(The directions only say 2 treatments, which will be enough to lower the numbers but not get rid of ALL the bacteria. Hmmm, so they’ll be back to dangerous levels in a couple of months or so, then you’ll need to buy more of their medicine. Am I too cynical?)
Hope that makes sense, Good luck.