Seems to me it could be a parasite infection that they both have.
Firstly you need to ensue you water quality is good.
If they are large the good news is that not eating for a week alone isn't that big a problem for them, so you do have some time.
If it were my tank, I would change 25% of the water right now, then again in two days, then again in two days. That should really help the water quality. One water change may not have a lasting effect as it tends to stir up more stuff, so I have found that doing a rapid series of changes as I have just described does a lot more good but is less harsh than changing say 80% of the water all at once.
Do not try to stuff them full of food right now to get weight on them. Do it gradually.
Personally, I would try and source a "parasite killer". As many of these are very hard on the fish. My philosophy is to make the fish's environment as good as possible so that the fish can fight off the infection. The other problem with those kinds of medicines is that anything that just goes into the water of the tank is unlikely to do much, plus
you are going to need a ton of it if you have a large tank.
Also if you add medication to the water, make sure you remove any carbon filter media as this will absorb the medication.
You really need something that goes into the gut of the fish. One way to do that is to soak the fish's food in the medicine.
However, you have to be very careful not to overdose the fish, but if things are desperate, it is worth a try.
Of course, the hardest part of all of that is that when things are desparate, the fish tends not to want to eat so he won't eat the medicated food.
One remedey seen on another forum is
Jungle's Parasite clear from Petsmart.
Link
www.junglelabs.com/pages/details.asp?item=TB636
Also below is extract from another forum.
Intestinal problems in general - like bloat and hexamita - are very difficult to treat.
I have had 100% success with the following metronidazole treatment:
1. Slowly increase temperature to about 82 to 84 degrees. Met was designed for use in the human body and will not be as effective at lower temps. I've dosed for 10 days at almost 87 degrees and my cichlids handled it without a problem. Just make sure to slowly increase the temp over a few day and also increase surface agitation or aeration to avoid oxygen depletion at the higher temps.
2. Remove carbon from filters. Perform a 33% to 50% water change.
3. Add back in 1 tsp of epsom salt for every 5 gallons of water.
4. Dose tank with 250 mg of dissolved metronidazole per 10 gallons of tank water.
5. Repeat steps 2 through 4 for three to five days or as soon as the fish starts eating again. At this point, begin soaking your fish's food in the metronidazole dissolved in warm water. (about 50mg per tbsp of water). Continue soaking food for five to seven more days.
I buy my metronidazole online from Drs. Foster/Smith. As NimbusV stated earlier, it is also sold under the name Flagyll.
Another Extract
Actually white stringy poo is often a sign of internal parasites, Pimafix is a great medication that will help to treat this issue. Normally white stringy poo doesnt come after treatment, it's normally a sign that something is wrong in the intestines of the fish. It could be something with what you're feeding him, it could be something such a decor or gravel that may of had something in it/on it that could of gotten him sick.
My 7" EBJD had white poo after I got him, and I treated him with Pimafix and it cleared him right out, and now's he is doing fine.
I am no expert but I hope the information I found may be of help, feel you need to source an aquarium parasite treatment and wish the best of luck..............
