I've been interested in mantis shrimps for a long while now and finally set up a small tank for one. I bought an 11 gallon via aqua tank w/ a power compact light perfect for nano-reefs. jury-rigged a lifeguard FB300 fluidized bed filter onto it and cycled the tank. when the tank was ready I put a small pistol shrimp in and he was happy. a week later nitrates were still very low so I added a few very small green mushrooms to the rock. I originally wanted to get a squilla type spearer mantis but to date have only seen one once in a shop, so I settled for a huge 6+ in. O. scylaris that cost way too much and had those brownish sun-burn sores on it's telson. it shed the skin within a week and seemed happy, but reluctant to accept any food. the color was decidedly yellowish green but the sores were gone, with only a little remaining marrs. he only accepted goldfish if I persistently shoved them in his face and even then reluctantly. the store I bought it from (aquarium city) said he scarfed on red fiddler crabs, but that wasn't the case in my tank. this morning i tested pH, ammonia, nitrites, salinity, nitrates, and kH. ph was a little low, ammonia nitrites, and nitrates were all 0, even after slight adjustment last night salinity was slightly high, and kH was fine. tonight about 9:00 the mantis was on it's back feet out and slowly moving it's swimmerets, the red fiddler crab was way up high on a rock next to dead, the pistol was dead. larger isopods were all dead and within an hour the mantis retired into it's hole to die. commesal crabs on a turtle weed rock were also dead, but smaller copepods were all seemingly fine though. also minescule (like almost ich size) white critters were all over the glass towards the top, having a field day. I'm sorry this was long winded but I'm at a loss here. any reason all large inverts in a tank would die?