Trying to prevent complete tank-kill!

Question
Hey there!  I have a quick question that's really worrying me.
But first, I have a 10 gallon freshwater with a millenium 1000 filter, filter last changed 3 weeks ago (but removed for the past five/six days for ich treatment).  i also have an air pump and strip bubbler and heater, temp is set at 72oF.  I use standard flake food and some algae rounds for my pleco.  Tank currently contains five 1.5 inch comets (feeder fish rescues!) and 1 sml pleco.  I perform a 30% water change every saturday under normal circumstances.  Tank has been cycled since early december 2007 without problems, however was not active for the three day trip from home to my dorm.
I decided to add a pair of african dwarf frogs to my tank after the unexpected (and still unexplained) death of my old pleco, who'd been eating fine and active until one morning i found her belly-up on the bottom.  the two dwarf frogs were accompanied by another pleco, who i realized during quarantine had a very strange red belly.  it went away a few days after it came home so I thought nothing of it.
the tank was fine with the new bioload, and to keep up with the added wastes i upped my water change percentage to 50% every week.  i also removed the frogs from the tank and fed them pre-soaked bloodworms in a separate container before putting them back in the 10 gallon to keep down on waste and be sure the greedy goldfish didn't snatch all their food before it got to the bottom.
about four days after they came home one of the frogs died, which I expected since it had trouble swimming (i think it had some kind of spinal damage).  but a few days after he died the other frog basically exploded.  i came home and found the corpse floating in the bubbles above my airstone, bleeding out its eyes, mouth, and vent.  the body was completely emaciated, ribs protruding, and clearly had internally hemorrhaged something fierce.  i removed it promptly and did a 50% water change 2 days in a row.  the frog had been eating normally and swimming well right up until its (gruesome) death.
About two days after the frog died my pleco showed those tell-tale white spots of ich, which i began treating the following day.  i followed manufacturer's instructions EXCEPT that i neglected to do a 50% water change on the second day of treatment- bad choice.
after 3 days of ich treatment i noticed that three of my comets (one albino, who's always been sensitive, and two orange/whites; the red/black ones weren't affected, oddly) had fin rot.  the pleco still had those white dots.
a few days later and i'm at my wits end!  although the pH crashed as a result of not doing the 50% water change with treatment thrice-daily 40% water changes, salt baths for the fin rot fish, and continuing treatment for the pleco's ich has done nothing for my tank.  four of my comets are laying on the bottom in the corner, and only move if i open the hood (expecting food), at which time they're very normal and active.  they return to the corner after about 2 minutes.  the fifth comet is standing on its tail at the surface between the heater and the intake pipe for the filter, and is harder to 'rouse'.  the pleco is fine and active, however, even despite still harboring those white spots.  one of my comets is flashing/scratching.
my pH has been corrected, my ammonia, nitrite & nitrate levels are back to normal, and i'm doing 25% water changes daily, and i'm still continuing my ich treatment even though the meds boasted a '2 day cure' 6 days later... so what on earth happened to my tank?!
i wouldn't be crushed if the feeders didn't make it, but i want to be sure that my cycled tank could still house new fish and the existing pleco.  later today I'm picking up some meds for the finrot and other parasites (did not have opportunity to do so earlier), but honestly if the fish are 'past saving' is it a good idea to further corrupt the cycling process in order to treat them?
I'm just left with a real head-scratcher here.  No one can seem to help me, Christy, I'm turning to you!  =]

Answer
Hi Chris
My apologies for the delay in answering your question...computer problems and I was unable to get online....

Sounds like a lot going on in that short time.  Let's start with the overstocking issue.  It's easy to overstock a tank, especially with goldfish and plecos.  It's recommended to have at least 15 gallons for one goldfish-granted yours are still small, but they do put out a lot of ammonia naturally.  Ich will show up when a fish is stressed, whether from poor water quality, being bullied, cramped conditions, being moved, etc.  It's also possible it was brought on by one of the new fish that was added.  The fin rot is a bacterial infection, again can have the same causes as ich, though it's usually a water quality issue.  Now, some ich meds will kill off your beneficial bacteria that's developed-causing poor water quality.  So, not sure if you have a test kit for ammonia, nitrite, and nitrates-if not I'd strongly recommend picking one up and monitoring those along with the ph since you mentioned that seems to be fluctuating-and that doesn't really sound normal either in that short time frame.  
 
The frogs...not really sure what happened there.  I do know that frogs are susceptible to water quality and can get a lot of the same infections/illnesses that fish get-like dropsy.  Did the fish look swollen before you found it "exploded"?  I guess it's also possible he got swollen after he died.  

Also, probably too late now, again my apologies, but it does sound like your overmedicating a bit.  At this point, I would recommend just doing a water change, and monitor the water parameters I mentioned above.  Fin rot will clear up on it's own in most less serious cases, if the water quality is kept good.  Also for the ich meds, most treatments need to be done for about 3 weeks-depending on the temperature in the tank.  And keep in mind, a lot of fish-including frogs and plecos, are sensitive to the medicine in the ich treatments. Here's a few links about ich and causes/treatments to look over:

http://en.wikipedia.org/wiki/Ichthyophthirius

http://www.peteducation.com/article.cfm?cls=16&cat=1791&articleid=2421

Again, I would do a water change, check the water parameters, and take a "breather" from the meds at this point, and see what's going on and where everything's at.  Overmedicating can be just as bad for the fish as the disease it's supposed to treat.

Good luck!

Christy