Join Date: Nov 2004
Location: PA/MD/DE tristate area
Good chance your nitrate test is under reporting and your nitrate levels are killing them, these are just eaten on the back end because the shell is easier to get through under the belly for others to eat, then they eat up into the head as they can reach.
Either get a new nitrate test, or take nitrate test bottle number TWO and bang it and mix it for about 5 minutes, then retest, see if the number goes up. The solution in bottle number TWO tends to crystallize and go out of solution, rendering the test results too low. That all the other numbers look fine, and that you have a SLIGHT nitrate level, and the odd death, consistently, suggests nitrates might be the cause.
If you're using API nitrate test and the tube turns orange or above (anything past dark yellow), it's the nitrates.