Cory(s) with sunken stomach(s)

[Temeraire]

I've had one albino cory develop a sunken stomach, and I only noticed when it began showing other symptoms such as refusing to eat, lose of balance and a lose of energy. This cory died.

Now I have another albino cory, maybe two that have sunken stomachs though the other symptoms aren't present. What might be the cause of this? I'd be a little depressed if they died as I also had a betta die around the same time due to dropsy (not sure of the direct cause) as the cory and these are kinda the only two fish I have atm.

This is a 10 gallon tank. The only other residents are an apple snail, a fair number of ramshorns.
Params: Ammonia: 0 ppm, Nitrite: 0 ppm, Nitrate: 0 ppm, pH: 7.4

Nitrate is where it is because of the plants in my tank, and with the current low bio load they're probably going to start starving...

 

[serissime]

I had a similar question a few days ago regarding my pygmy cories and I was advised to start a deworming treatment like Gel Tek Ultra Cure PX .... however I'm having trouble getting a hold of it... thinking about PraziPro but not sure yet....

 

[Lupin]

Go with Prazipro first for suspected internal parasites but if this is internal bacterial infection, then we have to go with medicated foods. Another alternative is combining kanaplex or tetracycline with the food they eat assuming you can get them to eat.