Dwarf puffer thin, not eating, breathing heavy

[Black_Rose]

We've had a pair of pea puffers in a 10 gallon for a month.
Tank has Amazon Sword, guppy grass, and java moss to break sight lines.

I've been feeding small snails from my other tanks as well as frozen bloodworms.
The other puffer is eating fine. I've seen it Chase the sick one away but not attack it.

Yesterday I found one of them laying on the sand, looking quite thin, and breathing heavily.

I've tried putting snails and bloodworms in front of the puffer, but it's not interested in them.

On Sunday I put the puffer in question in a 2.5 gallon tank and am treating the tank with PraziPro.
I put some small snails in with it, but it's still not showing any interest.
Also tried frozen daphnia and some frozen bloodworm.
I did see it take some daphnia but then spit it out.

It's swimming around occasionally but is hiding behind the heater or under the java moss most of the time.

Everything I've read seems to indicate the outcome won't be good at this point.

The only other parasite medication I have is Seachem Metroplex. Would that work better than PraziPro?

Any suggestions on what else I could try?

[Black_Rose]

Got home from work to find that the little puffer had passed away sometime during the day 

[matttimms49]

Sorry to hear this, losing a fish is always sad maybe you should check the water parameters in the 10 gallon to check things are ok in there.

[Black_Rose]

Today is water change day for that stack of tanks.

Water tested 0 for ammonia and nitrite, 5 for nitrate.

[Black_Rose]

Another sad update.

Our second puffer passed away today, exactly 5 weeks after the other one had passed.

This one had been treated twice for internal parasites and still didn't make it.

Very frustrating especially considering they have such great personalities and so curious little fish.