Hiya avnera and welcome to Aquariumadvice.
Continue to do daily partial water changes if ammonia levels get above .5 ppm
until the tank cycles fully and ammonia AND nitrItes both read zero. If you have levels of ammonia theres a good chance nitrites will show up (although occasionally they don't). Once that happens, weekly or biweekly water changes to keep nitrate levels below 40ppm should do you fine.
I do have some concerns about the surviving fish; first off what sort of catfish do you have? If they are cory catfish, they should be fine in a 26g (although they are schooling fish and would probably appreciate some buddies once the tank cycles). If they are common plecos they will get to be around 2 feet each (!!) and are going to be way too big for a 26g. Silver dollars will get to be around 8 inches long each (and around 8 inches high) and also will be too big for a 26g tank.
Oh, and that Cycle product? Is pretty useless. I'd suggest not using it; the ammonia levels might even be coming from that and NOT from the fish! I know the one bottle I had (before I dumped it) had nitrate levels over over 100 ppm
from the bottle, and I've spoken to other folks who had tested the Cycle and found it contained ammonia!
aka Cycling Guru and the Ich Slayer
*glares at Terry and QTOFFER*
Card carrying member of FTAS & GCAS.