Last week I could see something a bit odd with my shrimps but could not put my finger on it. Then some symptoms appeared in my snowball and green shrimp... their colouring went opaque and then faded, they started moving about more slowly. Then after a few days they were just lying on their backs and a few hours later were dead. Happened to just a couple, so I thought it would pass. Bad thinking! A day later my 9 amanos were all huddled in one cluster 2 inches from the top of the tank, and yesterday they were on their backs on the substrate, then by evening most of them had died, and more greens and snowballs passed away. probably only have a few shrimp left in the tank now (I had a small population to start with). My 3 dwarf cories are active as normal, but their colouring looks a bit off. I guessed I have some 'toxicity' in the water. Yesterday I realised I had made a schoolboy error. Whilst my tetratec ex 1200 foam prefilter and filter itself were clean the flow from it was almost non existent.... the spraybar outlets were heavily clogged up. I added lots of emersed plants recently that were undergoing transition and shedding some leaves, so I guess this would have also put a strain on the filtration, probably enough to 'tip it over the edge' so to speak. What have I done to try and fix things? (overdue) basic maintenance really... I did a WC (50l of RO. tank is 160l). Removed the spraybar, flow is restored! Gave the filter and pre foam a clean. swished all the dirt up in the tank (there was loads! more than I have seen for years and it did not really show until it was in the water column). added some activated charcoal\carbon to the filter. I can not see what else to do other than keep swishing the dirt up so the filter can catch it all, and clean the pre filter every day to keep the flow absoultely tip top. and a water change if I swish a lot of dirt up. Any input gratefully recieved.