Problems with my ropefish

I currently have 5 ropefish in a semi community tank (also 1 fire eel, 2 irredescent shark cats, 2 plecos, feeders). Over the last couple of days, they seem to have some problem staying at the bottom of the tank. Their rears float higher then their heads, and they all ball together in the heater/filter corner. I have already lost one, a seamingly healthy female to unknown reasons. On the night before she died, she looked like the letter "L", her front half floating fine, and her backsids hanging straight down.
I do know that my filteration is more then sufficent, and all tested levels are within normal limits for all the fish in my tank.

On the advice of others, I have changed feeding from frozen bloodworms to live tubiflex, but only one ropefish has "come down" from the corner.

Satepus

Right now all of these guys are rather small, no ropes are longer then 10", eel at 5", plecos at 5" and 6", Irre. shark cats at 5".
They are split between a 90g corner and a 55g long tanks. I can also split again to a 40g long.
90g 55g
Ph @ 6.9 Ph @ 7.0
Ammonia @ 0.125 Ammonia @ 0
Nitrate @ 0 Nitrate @ 1
Gh @ 5 Gh @ 5
AquaClear 150g cascade Aquaclear 150g cascade
100g powerhead 100g powerhead

I am hearing constipation from a number of people, I think that this may be the winner. S, is there a special technique to getting them to eat the peas? I'm assuming uncooked.

I would really like to hear from somebody who has successfully treated this, because i really love these guys.

Thank you for your help, but no avail.
We lost all of them but one. It was horrible. My only consolation is that not one of the other fish in the common tanks show any sign of illness.
If anyone has any ideas for compatible fish for a fire eel/irredescent shark tank, I can move on, put this behind me.

I went with constipation/complications because of the lack of stress in my tanks. All of the fish in my ropefish tanks have been together for some months, actually about 7-8 months, with no extra stress.
Yes, I had a number of bottom dwellers, but I also had plenty of hide space, plants (though fake), and surface area. They all seemed to get along fine, ate at opposite ends of the tanks.
My biggest clue was the lack of ropefish pooping, followed by the slight swelling behind the head and midsection, which worsened over the few days I was trying to save them.

Spartan, thank you for your advice. I have been able to get my one remaining ropefish to eat raw, peeled, slightly squished peas from my hand. He looks like he is coming around, swelling has subsided, and he is able to keep himself on the bottom of the tank without locking himself under something.

Satepus