How is he doing now?
As Lilnaugrim said, if you have a fish that can withstand warmer water, then the easiest way to treat White Spot Disease (also called Ich) is to raise the water temperature to 30C (86F).
Ich is caused by a parasite (Ichthyophthirius multifilis
). It can't reproduce in warm water. So by raising the water temp for a long enough period of time, it'll eventually die out.
The white spots that you're seeing are from parasites that have burrowed into the fish. While they're burrowed into the fish, they're protected from harm. They'll eventually fall off, but it takes a few days. So it can take about 5-6 days to see results using the heat method.
There are some strains of heat-resistant ich now, unfortunately. So if a temp of 30C (86F) doesn't work, try raising the temperature another degree to 31C (87-88F).
Here's some additional info about Ich, in case you want to know more.
There are 3 parts to the life cycle of Ich: Stage 1) trophont
- this is the stage where you see the white spots. The parasite has burrowed into the fish, where it's protected from treatment (which includes medications, salt and heat). So treatment isn't effective here. This stage lasts several days. Stage 2) tomont
- the trophont finishes feeding, and falls off. It's now called a tomont. Since it's in the water column, treatments (medications/salt/heat) are effective now - BUT only for several hours. It then forms a protective cyst around itself, so treatment isn't effective. Unfortunately, the organism is reproducing during this time. Stage 3) thermonts
- Several days later, the cyst bursts, and lots of new organisms go in search of a host fish. They have several days to find a new host, or they will die. Treatment is effective during this time.
So basically, you have to treat while the parasite is either in the early part of stage 2, or during stage 3.... Because the parasites go through three stages, you'll need to continue treating for at several days after you see the last of the white spots disappear. This is because the parasite is only visible during stage one. There are other parasites in the tank going through stages two and three, (but you can't see them,) so you need to continue treatment until it's gone through the entire life cycle sequence.