I have had a planted Biorb Flow for about six months. For five of those months I've had six happy algae eating shrimp keeping things clean. No other fish in there. The tank is moderately planted with a piece of wood and my own rock instead of what comes with the Biorb which I thought was just ugly...anyway..When I make water changes, I've done about a fifty percent change (basically to get the tannins out of the water from the wood). I make the water changes about every three weeks. I've used water from my kitchen sink filter as we have softened water in the house, and our drinking water comes through a filtration system that is post softening. We just changed last week to a potassium tablet vs the salt we have had previously. I made the change yesterday, and this mroning all six japonica shrimp are very, very dead. I've had several planted tanks before, I dosed the water with AmQuel and the temperature of the water was fine...Was it the potassium that did it? They have never had a problem with any of the water changes previously. I can't find any articles that say potassium is a problem. Anyone have any insight? I had cleaned the filter about two weeks ago. All the test strips look within parameters too.