Stringy, white feces may also be a sign of a growing
Hexamita type infection. That possibility is
especially possible of the fish aren't eating or they
only nibble and spit out food.
Hexamita (and a host of similar wee beasties) reside
in the gut of fish all the time. A hiccup in the
aquarium's water quality allows them to multiply, they
aggravate the lining of the fish's stomach and throat
and can eventually cause the fish to starve.
While what is effecting your rainbows might be fish
TB, I would first try picking up the frequency of your
partial water changes and either medicating with
Metronidazole as per the manufacturer's instructions
or putting them in a 10% Metronidazole bath for about
7 minutes or until they show stress.
If others on the RML have actual experience with that
bath and I have been advised incorrectly, please
correct that suggestion.
Terry Fairfield (A Commonsense Guide to Fish Health -
Barron's Educational Series) has also suggests a diet
rich in the vitamin B complex. Maybe feed worms
(white, Grindle, diced African red) which have been
fed on yeast.)
Hexamita can be cured. Fish TB can't. I don't think it
would hurt to try dealing with the former first.
All the best!
Scott