I've had my GSP for a few months and I absolutely love the little guy. He was young when I bought him (judged by his small size).
I researched on GSP for months before i ever went out and bought one. I started with a 10 gallon because I read when theyre young they don't mind too much, but I had him in there for only a month before buying a 30 gallon which he LOVES. They do require marine salt which started young they can thrive in freshwater but need to be gradually introduced to salt until they're bigger and older when they can live in a full marine environment.
I've had him with 3 tablespoons marine salt per gallon since i have had him and i'm about to increase it. but he has been doing great in that amount. GSP can put up with ranging salt amounts which is a lot less stressful. Make sure to ask the fish store how much salt they put in so you know what to start it at and stuff. and make sure you ask how much MARINE salt, not aquarium salt. When I bought mine they told me to just add aquarium salt and he would be fine because that's what they do...which I knew was wrong but I took him home in the freshwater since that's what he was used to then gradually added little salt with water changes.
They are messy eaters.. I do a 10-15% change every week. I feed him frozen brine shrimp and frozen blood worms. I actually melted them both down together and cut it up so that he has the variety everyday. I feed him a snail every week to keep his beak worn down. I had bought a couple ghost shrimps for him to snack on but surprisingly mine has left them alone which is fine because they're a nice clean up crew. Not many cleaners can survive in the brackish but my shrimps have been doing perfectly fine! They can't really live with any other tank mates due to their nature of being aggressive and fin nipping!
but good luck! you will fall in love with your little guy for sure!
my local fish shop also told me it's pretty rare that they get to 6 inches, but they can live 2-3 years!
Oh and make sure to have lots of decor and plants! they love hiding and are very curious fish. I have a lot of artificial plants because not many live plants can survive in brackish, but I do have java moss which has been doing great! I also have a log cave thing i got from petco that he goes in at night to sleep, he's like a little puppy.
They also sleep on the bottom of the tank which scared me when I first bought him because I thought he was dead!!
/badmanstropicalfish.com/brackish/brackish.html this helped me a bit about a brackish aquarium and setting up my tank!
