You have started treatment, using WS3. You either need to continue this, following their instructions, or do a couple of major water changes to remove as much of the medication as you can and then use another treatment (I'll come to that). On no account combine different treatments, this can make things much worse.
Any treatment will cause stress to fish, but when one is dealing with disease it becomes necessary to achieve a cure. The most effective treatment is the one that not only deals with the issue effectively but minimizes additional stress to the extent this is possible. I've never used WS3. The ingredients in WS3, according to their website, are malachite green, acriflavine and quinine sulphate. These are not easy medications for tetras particularly. I would myself use salt and heat. If you do a couple of major water changes (70-75% of the tank volume, vacuuming the substrate thoroughly) to get rid of WS3, you could move to salt and heat. I'll explain the process.
Leave the substrate (what's there now, just clean it well). Raise the temp gradually (use the water changes partly, depending what the present temp is--you do not want too much of an increase suddenly) to 86F/30C. Get to this temp within a day. no more is needed. Make sure you have very good water movement, with good surface disturbance; increase the filter to achieve this, or add airstones. At the same time (after all the water changes), begin adding salt. Use regular Aquarium Salt. Do not use table salt, marine salt or rift lake cichlid salts. Add 2 grams per liter; 1 level teaspoon is approximately 6 grams, so this would treat 3 liters. Take into account the displacement of water by substrate, wood, rock, etc. This is usually 10-15% of the tank volume. Dissolve the salt completely and pour in the salted water. Add it gradually, over several hours.
Maintain the heat for two full weeks, then turn down the heater and let the tank cool gradually on its own back to the normal temperature. If you do a water change after the first week (you should), add salt for only the water replaced. Do another water change at the end of the second week, 60-70%. This will remove much of the salt, the rest will disappear with future normal water changes.
Byron.
