GSP stopped eating, black stomach
Hi. I have a juvenile, about 2-3", green spotted puffer. Have had him for two weeks, when we first got him he was very happy and active. Wouldn't touch the frozen blood worms but attacked and devoured any snails we put in. Also started feeding him live super worms (as that is what they were fed at the store) and he loved them! Would gobble them up as soon as they hit the water. But just recently he has lost all interest in the super worms and snails.. Tried giving him pieces of shrimp and he got excited, took one bite then left it alone. He is still fairly active, swimming around a decent amount but has had a black stomach for a few days and no longer recognizes or follows you at the tank. He also seems a bit over reactive and jumpy.
He is in a 75 gallon tank with lots of decor, 1 large discuss, 2 medium discuss, a very large catfish and a large plecostomus. The water is low end brackish, levels are all fine, 0 nitrite, 0 nitrate and very low ammonia. Just did a 25% water change and do one every few days.
Please let me know if anyone has any suggestions I really want this guy to get better :/ all other fish are fine.