Review on Biohome Ultimate Filter Media Aquarium by Julie Bishop

I added this to my 250 gallon tank. All reviews about him were amazing. I did my usual tank cleaning with a 20% water change. The only thing I've done differently is my canister. Two hours after adding it, my nitrate levels were off the charts and my pH was extremely high! That night I changed another 20% of the water and went to bed for two. When I woke up the next morning I found that 2 of my 6 inch African Leaffish were dead. I removed them from the tank and did another 20% water change but noticed that all of my fish went to the top of the tank for air. Whatever it was on it, even after I flushed it, they killed my whole tank! I've lost 4-6" Leaffish, 3-5" Kissing Gourami, 10" Plecostomus, 3 Blue Gourami, 4 Sunset Gourami and 4 Gold Gourami! I'm devastated! I've had most of these fish for over 8 years. I've never had a problem with it!