Greeting, new puffer parent here

[Timber]

Hello all, Its great to have found a place to answer some of my question i have now and I know more will come as she/he grows.. I acquired my green spotted puffer from my daughter who could not let the store flush him as he was a return and they cant put him back in the tanks. So here she comes home with him and we dont have a tank up.... Knew he would die if i did not get it cleaned and up so I scrubbed it in hot water and got it going.. minus the filter.. we seem to have lost parts in our recent move.. Cant get a new one till monday or tuesday soooo I figured just keeping the water cycled out for fresh would help more then leaving him swim in it till i get the filter.. Did the first partial water change today but It seems to have stressed him.. Is this usual for a puffers first change in his home?? Only other fish I ever keep were goldfish, angels, mollies, tetras ect (freshwater).. so this is all new...I only have a 2 gal right now but he is only 1inch long so Im hoping I have a little bit of time to get a 20 gal. But anyway the reason I decided to do the partial water change today was because there some bits and pieces of brine shrimp still in there and he did not touch the one i gave him yesterday morning.. which also brings up a question... how often should I feed him the brine shrimp?? should I get some plankton and bloodworms on monday or tuesday and mix it up?? give him diff stuff each day??
Thanks all and I think i will be here a lot with tons of questions lol