Hey all, so I'm trying to get a few quick opinions on my new 310. Quick run down is it was definitely used as a reef tank before I got it, and sat for 2 years empty in a garage before I picked it up. My girlfriend cleaned it pretty well using white vinegar, and it sat empty for about 2 months before I got it set up and filled. I used 150 pounds of quikrete playsand for substrate, filled the tank, hooked up a canister filter to clear the water a bit, and also act as the sole temporary filter until I plumb the sump up. I got it filled last night, and as a test put my bullhead catfish in to see if everything was going alright. He seemed just fine so I dropped in 2 black crappie and 2 yellow perch. NOW the problem. Within 2-5 minutes, the fish were heading to the top and acting extremely lethargic, and within another 5 minutes I had one black crappie on its side at the bottom. I fished them all out and back into their temporary holding container and they were just fine. My question is, am I looking at excess salinity causing the problem or a lack of DO in the water? I had an air stone and also the return from the can filter above the water line to break surface tension. Just looking for opinions before I drain 300 gallons of water into my yard and try again haha. THanks!