i have a 10 gallon for cherry shrimp also, sometimes i'm like 'WHERE THE HECK IS EVERYONE?' and i can only spot like 20 of them and sometimes there's like 40 all right there in plain sight. yours are prob especially hard to see against the tan gravel right now.
could the shrimp parts you saw be molting? were they clear/white?
i dose excel, iron, and trace into this tank with no ill effects. PH 7, temp 73-74
4 * 8 * 15 * 16 * 23 * 42