why did my bamboo shrimp die?

[Whitney]

Hi,

I have a 1 year old 30 gallon tank. It currently houses:
6 espei rasboras
2 diamond tetras
5 sidthimunki loaches
1 albino bristle-nose pleco
several little snails that hitched into my tank on a plant several months ago

over the year I have had and lost:
5 german blue rams (I love them, but have now given up, as I couldn't keep any alive longer than 4 months)
a 3rd diamond tetra (I will eventually replace him)
several freshwater schooling gobies
several cherry shrimp (I've found only two dead, most just disappeared-probably eaten either before or after dying- I now no longer see any in the tank)
1 bamboo shrimp:

The bamboo shrimp is my most recent and upsetting loss. I got him just after my tank first cycled and he seemed to be very healthy and happy all year. I don't know why he died. I went away for a weekend (Friday-Sunday) and when I got back, he was dead.

I checked my water parameters. The ammonia and nitrite level is 0, my nitrates are at about 20, and my ph is about 6.8 (which is normal here). I keep the temp set at about 79 degrees.

Recently, I've had a small beard algae bloom (nothing overwhelming).

I did a water change last week. As usual, I treated the water with stress-coat.

Was I doing something wrong? Why did my shrimp die?