Rainbow fish

[Megfish]

Hi All.
I was wondering if anybody could help me.I have a Rainbow fish that is really quiet big and yesterday i noticed a disturbing new development.
This fish is swimming around with a stringy bit that looks like intestinal lighning hanging out its butt.I read awhile ago about a disese that does this and that it is prevelant with Angel fish.My big Angel that died a year ago died of this disease i am sure of it.If somebody nows what it is and are able to tell me what to do to fix it would much apreciated.
Our tank is a community Tropical tank 180L
Ammonia 0
Nitrites 0
Nitrates 20
I have done a water change yestery and do 25% weekly.
I also read that it is deadly if left.
All my other fish are good.
Cheers

 

[tttnjfttt]

It sounds like it could be internal parasites. Do you feed him any live or frozen foods?

 

[Megfish]

Yes they are fed frozen blood worms or frozen Brine shrimp the type that are purchased at a lFS.They are also feed flake and pellets for my bristle nose but they come and swallow them before they reach the bottom some times.
Also Ph of 7.2
Kh of 5
cheers