Yes, I agree pretty much with the above. 10G is far too small for two GSPs and really is too small for one beyond the early juvanile stages. Once they get 2.5" or so it's time to move them to something bigger, and they'll likely be really bored long before that even with heavy planting and snails / ghost shrimp to hunt. My lone GSP lives in a 29G with lots of plants to break up line of sight / make things more interesting and she is still only about 2.5" but I have moved her to high brackish. There is a small pleco in there to help with algae and she pretty much ignores it, but it has been in there since she started in the 10G. Never acknowledged it.
I did make the mistake of getting a second GSP when mine initially got bored in the 10 gallon (lots of 'pacing' up and down the glass, didn't change if I moved plants around) but she bit his back fin twice and I returned him to the local fish place the next day to avoid further injury / agitation. The pleco was his replacement, and while I check him for missing fins daily I've never seen any damage. I keep my GSP really well fed, probably over-fed, so that helps -- she feels no need to snack, and he's definitely no threat / challenge to her, so they leave eachother alone. The pleco does get annoyed with her constant 'buzzing' sometimes though, and will lap the tank a few times in frustration.
Also important to note is that GSPs like all puffers are really messy eaters! Filter, filter, filter. I had a Marineland Penguin 350 (rated for 70 gallons) on the 10 gallon and will soon be ordering a canister rated for at least 100 gallons to supplement it on the 30 gallon. I'm probably taking over-filtering to the extreme (no issues with water quality as it stands, have never had any) but you can't do any damage with an over-abundance of filtering and can easily kill a fish as sensitive as a puffer (being scaleless) with bad or even middle-of-the-road water quality.