The 37g will only be large enough for a single GSP. Picture a Nerf football swimming in there! That's how big an adult GSP gets. Even as juvies, I wouldn't keep more than one in a 10g & that's only while it's <2". Please do not buy any more fish for that tank. I suggest moving the 2 puffers into the 37g tank ASAP.
Also, GSPs & F8s need different salt requirements. GSPs going into high-end BW & even better--marine as adults. F8s live longest at low-end BW SG of 1.005.
GSPs grow to 3x the mass of a F8 & is generally much more aggressive, so they don't make good tank mates for each other.
http://www.**************.com/forum...cus/an-introduction-to-green-spotted-puffers/