Pea puffer help?

Hey guys, I got some pea puffers from someone on a group who wasn't looking after them properly, I set up the tank in a rush but I took water from one of my already well established tanks and added that into the new 30x30cm tank (all I have at the moment, will upgrade as soon as I can) with a heater on 26 degrees celcius, and a new small filter. They seem lethargic, I just went to go fetch them and I just really want the poor things to survive.

Any advice for a first time pea puffer owner? I also bought frozen blood worms, how often should I feed them? There are 4 of the, they still look quite young. I'm currently climatising them.