Angelfish: Not eating, hovering in one spot, laying on bottom of tank, white poop

[kmj0070]

Hello,

One of my two angelfish in a 20 gallon, heated, filtered tank has been acting strange for the past week. At first, he began to hover (upright) in one spot towards the bottom of the tank for the majority of the day and has been breathing fast. Then, a few days ago, he began to sporadically lay on the bottom of the tank which resulted in less labored breathing. When there is any external movement near the tank (a person or a dog walking by) he resumes swimming normally for a couple of minutes. He hasn't been eating and he has had a number of white-ish fecal excretions. I have a number of medications on hand, but am unsure of how to treat him since his symptoms could be caused by a whole host of different conditions.
The other female angelfish is acting entirely normal and not exhibiting any of the same symptoms. Here's a little bit of information on the tank.

-Tank was established a little over a year ago
- Heated to 81*
-PH: ~6.5-7; Ammonia: 0; Nitrite: 0; Nitrate <20
- Aqueon Quietflow 10 filter
- 25% water change last Monday, 10% water change yesterday (dosed with seachem prime and API stress coat and I ensured the water temperature was *80-82* prior to adding)

Pictures of his two most recent positions attached.

 

[Autumnsky]

The hollow stomach part of the belly looks like it would be internal parasites. This fish could still be savable. Online Angels Plus medicated fish food would be helpful for the fish. Check with a local fish store usually most do not have the medicated flakes food.

I prefer the medicated flake food for the fish to eat. Using the liquid to soak into the food sometimes the fish refuse to eat so the medicated flakes are better imho.

Haven't used this myself but have heard good reports.
or PraziPro - Hikari Sales USA

But you might also check into using liquid fenbendozole (Safeguard Liquid Goat Dewormer) dosed into the water.