Tank parameters:

Temp 77.2

PH 7.8

NH 0

NO2 0

NO3 3-4 (darker than 0 but lighter than 5 on API Master test)

15gal Fluval flex 2.0

Stocking: 4 platys, 6 Danios, 2 anubias -unsure if plants matter. No plans for more fish but would like to add a nerite snail and more plants once my tank is more established. 

I use Seachem Prime and Stability with each water change. 

I have been treating the tank with ick guard for 4 days, blue platy had a white spot on its tail which resolved 2 days ago, I was going to do one more 25% water change and treatment today as there's been no signs of other sick fish or spots, until today when I work up and noticed this danio acting strange. Flared fins and swollen looking belly. Initially I thought it could be acting territorial but, then noted the belly remained swollen in appearance long after the other fish lost their little"breakfast belly's". 

I am worried that it could be dropsy but, don't see any pineconing on the scales or redness but, maybe that's just a late stage symptom? Also, the spine doesn't seem to be dipped down but, again maybe that's a late stage thing or, maybe I'm too new at this to see things that are obvious to the rest of you. Eating normally but, I'm worried about feeding any more in case it's constipation or something made worse by feeding. 

This tank is very freshly cycled so it's not mature, I've only been getting 0 ammonia and nitrites for 5 days after doing a fish in Cycle (not my choice, husband and kids went rogue at the fish store before I had the tank ready). 

We had 6 neon tetras in the tank who got sick but they were moved to a hospital tank on April 14th. They all died of what the fish store said was neon tetra disease, last one just died yesterday. I'm aware that we were over-stocked in the main tank initially. If the tetras got better, they were going to live in their separate tank.

Other things of note: 

Our fish stores do not take returns 

I'm in Canada which limits my access to fish meds

I don't have space to add a larger tank

I can buy things I need from Amazon Canada or PetSmart Canada online

Happy to provide any other info, that's all I can think of that would maybe matter.  

Sincere thanks from a mom who was thrown into being an aquarium / fish keeper. I want to do the best I can for these guys since they've been brought into our home. 

What is going on with my leopard danio?