Angels won't stay alive

I have a 55 gal freshwater tank for 5 months. PH=7.8, Ammonia=0, Nitrite=0, and Nitrate=20. 3 Danios (from original cycling) 3 Pepper 3 Julie Cories, 3 Clown Loach, 3 Platties, 3 Dwarf goramies, 8 Harliquin Rasporas and a bristolnose pleco. I also started putting plants in, (6 Java ferns and 3 amazon swords).
I would like to have 2 or 4 angel fish as my "focus" fish. But I can not keep them alive. They usually double in size in about 6 weeks but then get a pinkish/red color at the base of the pectoral fin and usually die 3-4 days later. I can't find anything on the web that may help me. I have taken the water to three different stores, two said nothing is wrong and one said my phospate was high (1.0). But that's how it comes out of my tap water.
Can someone please help.

http://www.petfishtalk.com/interviews/breeding_angels/ breeding_angels.htm

I found for you a lecture on breeding angel fish in aquariums.

Hope it has all the answer you need.

If not just tell me and we'll try to find some more answers.

Say, can you upload a picture of them with the pink pectoral fin?
A picture is better than a thousand words.

I tried to take a picture but they all come out too blurry

You can add phospate remover to the aquarium.

The picture probably too heavy can you resize it?

Try Again...

I have done some research and have reason to believe it is Hemorrhagic Septicemia.

It is a serious disease that can be caused by a bacteria or a virus and causes the symptoms you described. It is usually accompanied by sluggish behavior.

The other option is water contamination but if you say the aquarium is clean it is probably the disease.

You'll have to check the source of the angelfish maybe the supplier is not realiable.

Sorry I can't help more. Medication may work but the chances are 50:50.

You're correct about the sluggish behavior. They will hang out in top or bottom corner of my tank, won't eat, and then their fins start to hang. Any ideas why none of my other 27 fish are subjected to it? I got to run to work. I'm gonna research the stores this weekend. Thank you for your help

One of the reasons angelfish are not good in most community aquariums is they can catch diseases from other apparently healthy fish. In addition, they are a true "tropical" fish and thus do best in 80 to 82 degree water. A fish disease can stay in an aquarium for a long time, so maybe your best bet would be another aquarium specifically for angelfish. I can't say for sure, but some of your other fish could be fin nippers; some even do their dastardly deeds at night when you're not looking. Also, a conventional water parameter test will not tell you if there is a disease in the aquarium.