spiked ammonia

[ValHolla]

Hello,

I've been keeping these awesome shrimp for a little over a month now. I got the tank setup beginning of January, let it cycle until the beginning of March. No issues, only topping off with RO water when evaporations occurs. after I got my shrimp, they all colored up nicely after a few days to a week or so. then they all started to turn pale and clear. I did a little poking and this appears to happen if they are stressed (which makes sense.) I bought a test kit and the ammonia was super high, not lethal(just yet).... so I did just under a 50% water change.

I have not fed these since I got them, letting them eat the biofilm that accrued before I got them.

2.5 gallon tank has live sand, black lava rock, macro-algae from Petshrimp.com, 10 snails and 20 shrimp. what caused the ammonia spike?
my running theory is the live sand had something to do with it, I know zero ammonia/nitrite and nitrate is the target, but what is "too high"?

I'm running at 1.010-1.012 for salinity.

Thanks all!