Hi, My 2 puffers are approximately 6 months old now. I have them in a 50 gallon tank and I have them in Brackish water. I changed over from Fresh water to brackish approximately 2 months ago. I have noticed recently that one puffer is always grey on the belly while the second puffer has really brightened up with a more yellow appearance on his back. The bright yellow puffer rarely turns grey underneath (usually he's white) but here and there he will get a bit of grey. They do not fight with each other as the tank is so big they can hide on different sides. They sleep on opposite sides of the tank in their plants / hiding spots but during the day they seem to swim around together. I have been testing for ammonia levels GH, KH, PH, NO2 and NO3. Can someone give some advice on what I need to do to fix the puffer that is always grey? I don't want him dying. Test results as of 10 minutes ago Ammonia = 0.25 GH = 120 KH = 40 (i think that is pretty low?) PH = 6.5 (again, is this too low?) NO2 = 0 NO3 = 160 (I double tested as this number seems really high) What is going on? Are my readings way out of wack? How do I get the tank stable. I should mention I have approximately 10 ghost shrimp in the tank for food at the moment. Thanks in advance!