Sorry man I really wasn't talking down to you, I just wanted to get all of the information on the table before I started. I'm glad to see you have plans on a larger tank in the future, so that takes care of that one. And without the crab, that issue is moot.
Can I ask what you used to treat for parasites? IP's are nasty and very difficult to get rid of IMO unless the fish actually eats medicated food (which is normally difficult). Water-based meds don't work as flubenol is no longer allowed to be sold. I ended up using a dog dewormer from Petsmart that came as a powder that I mixed in with freeze-dried bloodworms. That seemed to work well and was the only thing they would eat with the medication (they can tell there's something in the food). Just keep an eye out as it can come back. Krill and shrimp are great foods. Try to keep the shells intact on them as it will help to wear down the beaks a bit but you may need some harder foods once they get larger.
My dwarf puffer didn't touch snails for almost 2 weeks! I was afraid she was going to starve to death, then suddenly, they were ALL gone. I swear she ate 20 in a day! If you keep a couple small ones roaming the tank they will eventually realize they are food and eat them.
Glad to see you're doing frequent water changes. Do you have a liquid test kit to measure ammonia/nitrIte/nitrAte? It's a good idea to have one to test every once in a while, such as now when they aren't eating.
You mentioned you knew they were brackish, does that mean they are in brackish conditions in the tank? Please again realize I never meant to do anything other than try to give some advice.
HTH