New Puffer Not Looking Good

So we've had one puffer for about 8 months alone in a tank. We added to more last week and added more plants to break it up. They chase each other a little but more so between the OG puffer and the littler one he can't catch. The third and middle one has taken to basking in the plants and we'd find him on a different plant from time to time. This am we found him laying at the bottom of the tank. I noticed his breathing has always been much more rapid then the other puffers. He doesn't look skinny but out of the 3 the only one that eats the blood worms is the OG Puffer. The 2 new ones go for the snails. So he could be eating them at night.

I've removed him and put him in a 1 gallon holding tank for now with some Stress Coat in there. Not sure if I should treat for parasites or not. Really don't know if anything is wrong with him as he was always a basking puffer but I know from previous laying at the bottom of the tank usually means the end is near

Quick strip test of the water shows
NO3 0
NO2 0
PH 7.0-7.5
KH 80
GH 60
Temp 76

 

Here is a picture of him in the holding tank

 

Does that tank have a filter and heater? Also he might just be stressed from the move, different fish react differently

 

How big is the tank?

 

It does not I put warm water in there and when I go home in a few hours for lunch I'll circulate tank water in there. This was just a temporary thing to get him away from the other puffers. I have one of those small breeders fishpen things I can put in the tank and put him in there but wanted to hear back if that was the right move or if parasites could be an issue

 

How big is the tank?

Main tank 15 gallons
Holding tank 1 gallon

 

Id put him in the net if there's no filter and heater in the temporary tank

 

Id put him in the net if there's no filter and heater in the temporary tank

I will set this up when I got home for lunch in a couple hours.

 

So should I keep him in the holding pen for a while? Put a snail in there?

 

How big is the main aquarium and how big is the net?

 

unfortunately this poor guy passed last night I had him in the net which was about the size of a 1 gallon tank(main tank 15 gallon). I had a plant in there for him to hide in to try and ease his stress. He laid in the plant most the day last night he was laying at the bottom of the net when all of a sudden he made a quick movement and then floated back down to the bottom of the net and he was gone

 

So sorry He was a beautiful little guy.