Ammonia reading has been high - measuring something like 1.0-1.5. Before this, highest reading after cycling was 0.1. I did eveything I know of - changed 1/2 the water; added carbon - no change. Tank is a 55 gallon with 72 lb lr & remora pro skimmer,, all up and running for 3 months. This came on suddenly, since last week's test showed 0.1 ammonia. One crab has died and one fish showing distress. Inhabitants are a royal gramma, clown, yellow tang, a few starfish, 3 shrimp & small snails and a bunch of small hermits. Nitrites are 0, nitrates are OK, ph a bit low at 8.2. Only change I can think of was the addition of several small hermits. Any advice as to how to get the ammonia down? Why didn't it go down after a 50% water change?