Hi this is my first post here and unfortunatly not a good one. I have had trouble in my tank over the last 2 weeks and my fish are dying. This is my first tank and about 5 months old. First it was an out break of ich which I treated with API white spot cure. I completed the treatment as direction on the bottle says but then 2 days later I saw no more spots another outbreak happened which looked the same. It first started on my cardinal tetras and then moved to my catfish. All the cardinals has died and the cat fish is not looking to good. I have a male guppy and a male betta in the tank as well and they seem to be unaffected (they don't fight and gets alone very well. betta is even leaving my cherry shrimp alone).
So for the disease, it started as white spots and now there is a mix of yellow as well and only on the catfish (about 2inch big). I did another course of API white spot when I noticed it the second time but that had no effect, I am now dosing with API primafix and API melafix. I am from UK so do not have access to all the meds you have in the US. Any help with identifying and helping me to treat this outbreak would be appreciated. I've had the catfish for almost 3 months now.
pH : 7-7.2
Nitrates: 0
Hardness: GH-14-17
Nitrite: 0
Ammonia: 0
KH/Buffer: 2-4
Water Temperature: 25°C 77°F