Understandable man, I like my fish but I love my frogs. I am the same way, if I lose a fish I am a little bummed but if I lost one of my frogs it would be like losing the beloved family dog..
Honestly though what fish are we talking about here? Not trying to judge but it may help if we knew what fish you had.
EDIT: My bad I missed your post about which fish!
Oh man! This is bad news bears.
Blue channel catfish are HUGE fish! I mean huge! Also aggressive! A 20 gallon is not near enough water for these guys and they grow fast. A goldfish is also a pretty messy fish and two is really pushing it in a 20 gallon with the goldfish alone. Now add the frogs to the mix and things are just out of control here, only the frogs themselves would be acceptable in a tank of this volume.
There is just not enough water to house all of these species!
I think the reason your fish are contracting Ich is because of the conditions they are kept, you just can't keep all these species together even with 100x the water volume these species simply cannot co-exist when they mature.
When I say a blue channel catfish is huge I mean too large for even the largest of tanks, I mean even 200 gallons is not enough to house a single specimen and you have TWO. These are monster fish dude!
I would ditch the fish and let the frogs live in the 20 gallon, the goldfish can be re-homed but I have no idea how you got blue channel catfish and I don't think they are even possible to keep in a home aquarium.. they belong in a river.
ACF are immune to Ich, it's a fish disease (actually is a parasite). I've had fish with Ich with ACF and they never had any problems, the fish were removed and I never treated the tank for Ich and it went away, Ich cannot survive without a host.
BLUE CHANNEL CATFISH
SCIENTIFIC NAME: Ictalurus furcatus
ADULT SIZE: 18 to 24 in (460 to 610 mm). The Alabama state angling record(111 lb) was caught from Wheeler Reservoir on July 5, 1996. The previous state angling record (104 lb) was caught in Wheeler Reservoir on the Tennessee River in 1994. During our river surveys, we infrequently collect and release blue catfish weighing 30 to 50 pounds; most specimens are 10 pounds or less.