So on my other tank I used plain ol' charcoal fiberglass screen. Problem I had with it was being able to see the false bottom in the water feature unless doubled/tripled up. So on my new 55 for the FBTs, I grabbed Sun Guard 90 because it had a nicer grid to it and felt thicker. Even one layer I cant see the false bottom. Well I have about 15-20 gallons in this tank with Fluorite from Seachem as the aquatic substrate. I used all the normal supplies besides the Sun Guard. I have a canister filter and all my readings with my testers are good (pH, Nitrite, Nitrate, Ammonia). I also use Stress Zyme. I have been trying to keep Danios in the water for a fish-in cycle and all the fish last about 3-5 days then seem lethargic and eventually laying on the bottom till they quit breathing.... I took water to the LFS and they confirmed my levels were fine and were adamant about water temp... Water temp is 71-75 at all times. Also I do have this clear slime growing on the wood in the water feature but I think it is just 'slime mold' and seems to be getting less abundant as the 2 Mystery Snails clean it up. The snails are the other things that have survived. All I can think of is maybe the Sun Guard 90 might have some UV inhibitors in it? I haven't been able to get in touch with New York Wire yet. I have the FBTs in another tank and am not going to move them until I know the water is safe. Any thoughts?