Help with my f8 puffer. Is my substrate hurting him?

[Mandalynn87]

I recently got a figure eight puffer fish. I did research the parameters water temperatures and what they eat but I was a little ignorant to other things. I'm quite ashamed to say it but I am here now asking for help.
I was kind of freaking out this morning as I saw my puffer fish practically attacking the substrate. I thought well is he hungry. Normally he goes flying super happy and excited and follows the tongues as soon as he sees them. He did not do this this time he just kept attacking the substrate. When I did get the Krill up to him he ate it quickly. I started thinking something was wrong , like maybe hes not seeing the tongs? I added a few drops of water conditioner.. not sure why.. thought well if something got in the tabk, maybe it would help. I did a API water test and everything was normal pH is about a 7.8 to 8. I know my water is generally quitw hard in my area. though I do not have a test kit for that. he is in freshwater we will be switching to brackish soon but I've only had him for about a month and I bought him in freshwater. He is in a weird 10 gallon. Hes not full grown and i had tank size restrictions. So i got a strange shape tabk that is short and wide. Its as much horizontal room as a 15 gallon.
The API test also showed zero for nitrates nitrites and ammonia or at least an unnoticeable amount for the color change.

The only new additions to the tank I've had is I added Java ferm, Amazon sword and Anubis Nana. Into the tabk. It was the kind that is snail free in the tube's they sell out of water at petsmart/petco. Most likely they will not survive the brackish change but since I am going to go low and brackish I was hoping if I gradually did the brackish change with the plants in there they might survive. That why i chose those plants. . I did notice that he took several holes out of one of the Java ferns as it looks like swiss cheese at the moment. I did see him do it one time, and he just spit it out.

I had to go to work but he did seem more normal by the time I left but my worrying led me to do some Google searches. I did see that bottom feeding and digging is he normal behavior. I feel like I feed him a lot but maybe he was hungry. I do worry about overfeeding but I'm feeding him twice a day with one day off to help with digestion, anyway Google search said that I shouldn't have Pebbles for a substrate and should be using sand or crushed Coral. My local tap water pH is at 8.0 normally or at least very close. I also did put some Coral rocks in there to help buffer just in case. So I didn't worry about getting the crushed Coral sand as I didn't want to over buffer.

I don't know... but im worried about bit.. I don't wanna stress him by pulling him out to change the substrate. I really like this guy I have a whole tank where I'm breeding Bladder snails Set up for him, he eats Krill bloodworms and bladder snails. He doesn't eat the bladder snails as often because I'm still trying to get the colony built up but he does get it a few times a week.

Sorry this is all over the place I'm using text to talk on my lunch break, but since I don't need the buffer of a crushed Coral sand for the pH is it okay that I'm using Pebble or is that possibly hurting him?

Again sorry for the run-on sentences I had to be quick on my lunch break so I use the talk to text. Have a great day

[Pufferpunk]

Sand is preferable. You don't have to remove him, just scoop the gravel out with a net.