Shrimp are dying, please help

[lexi]

I originally I had 13 shrimp to start off with and it's been around a month and they all seemed fine, molting from time to time. Then my parents just told me a few days ago (3 days) that when I was on my trip for a week, nearly a shrimp died every day. When I came back, the shrimp seemed fine and I didn't see any problems. Yesterday, I decided to clean the tank by sucking out some of their poop at the bottom of the tank that is always under the tiny black pebbles I put there (the filter doesn't filter anything). I was moving the pebbles around a lot and the black dust from the pebbles just whooshed up into the water and lingered there. The water looked disgusting. I had some tap water which I conditioned already so I took the shrimp (there were 5) and put them in that water. I cleared out all the water in that tank and filled it back with my conditioned water with the shrimp. My sister bought a new filter cotton thing to replace the old one cuz that has turned black from the dust probably. But today when I checked on them, the yellow ones had black stuff in their head, which has never happened before. They are still eating though. A red one just died. So I really don't know what to do. I know I shouldn't have changed all the water but I couldn't leave it there cuz the black particles were clouding the water. Someone please help!!

[Mustafa]

Unfortunately, it's likely to late to help in any meaningful way. You don't want to constantly clean a shrimp tank. In fact, you should *never* suck up anything from the substrate. Just leave it alone. As for particles in the water..they'll eventually settle. How long was the tank running before you put in the shrimp? Go get a kh test kit and tell us what your tap and aquarium water kh levels are.