oh my gosh. API test tubes are durable. I just dropped one and it doesn't have any scratches. Anyways, nitrites read 0 in both tanks.
By the way, before putting shrimp into this tank, the sand was clear of anything. I came back after 10 hours, and there are these brown dots all over the place. I don't know if you can see it, but I tried to take a photo of the sandy area. Is this poo? Is it good or bad that there is so much (there's around 20 "pellets" for a 1cmx1cm space, less as you move away from the one-eighth of a wafer that I fed them)
In addition, whenever I want to remove the wafer piece, a shrimp goes to eat a bit from it. Should I leave it in the tank, or remove it when I wake up (going to sleep in 30 min or so)