This is my first reef tank! I’m pretty sure it’s cycled, it’s growing diatoms. I cycled with life Rock, live sand, fritzturbo start and two clownfish (Also two snails.) I got my first two fish from petco . The smaller fish died two days later, mucusy,not able to breathe, I’m assuming it was brook. The larger fish was fine. I got a new fish the next day. (No QT tank because it was a new setup. Well the fish have been fine for about a week. Well today the larger (older) fish wouldn’t eat. He started hovering above the bottom. I did notice a long stringy poop? But that’s gone now. He seems to be breathing hard. The little fish won’t leave the bigger one so now he kinda swims circles around the bigger one. (The little fish appears to be fine and still eating, other than some weird jerky motions). What should I do? I just topped off the tank. And turned off the lights because it seemed to calm him down a bit. I added maybe 5gal worth of fritz a few days ago (to help the tank cycle). The ph seems really high even tho it has been fine every other time Iv check it. (Bigger fish is on the bottom).