Medicines for Protozoa and Worms

Hi there!!
I been lurking this list for sometime....thanks you all for all the tips!!
I have a planted aquarium(Co2..the works)and is doing great...but
my fish....Angels (Pterophyllum scalare) after many years of been with me
...5 years...one have suddenly died....jus went to the bottom...lost
buoyancy..ect ect and the other one ( out of 4) is looking kind of
shy...not eating..swollen belly....in the outside (skin) they
both look very healthy....so I am planing to give the whole tank
medicine...thinking that I have some type of Protozoan or worm
lurking their intestines and inner guts( I did not want to do a
necropsy on my first fish.....I felt sad )-:) 
So....Can I give them Hex-A-Mit (aquatronics)=active compound Metronidazole
or flagyl....same stuff they give out for Trichomonas sp in people...and
or Clout (Aquarium products) used also for parasitic infections contains
a bunch of other "azoles" with out killing my plants

The idea was to treat the whole community of Angels, Corydora sp.,
Plecostomus sp., Whatevergenus curviceps ......
Maybe I am over reacting...all the other fish seem fine...I do not
know the life span of angelfish...and I haved quarentine most of the fish with
ick medicine (formaldehyde) before putting them in my 75 gallon aquarium.
Please help! any suggestions are welcomed thru the newsletter or
by e mail to lpasarel at beach_utmb.edu

Lester Pasarell                               e mail= lpasarel at beach_utmb.edu
Medical Mycology Reference Laboratory                 ad727 at rgfn_epcc.edu
Department of Pathology
University of Texas Medical Branch
Galveston, Texas 77555-0609 
URL for the laboratory=http://fungus.utmb.edu/myco.htm
url for my page = http://fungus.utmb.edu/index.htm