Something is off here.
 

Tank is 2 months old.
live rock from LFS
live sand aragonite oolite
caribsea life rock

salinity 1.027
ph: 8.3
ammonia, nitrite, nitrate: 0 or close to zero

tank has been relatively healthy and generally happy with few exceptions.
around month one a diatom outbreak started, and last week i noticed a patch of green hair algae on the life rock branch

most recent change: my 27 watt par38 bulb got moved closer to the tank because of the arrival of my gooseneck (last week). previously i had used a desk lamp propped up on a box, but the gooseneck is only one foot, and it doesnt allow enough distance between the water and light.

also, 3 days ago, my water was noticeably warmer, and i noticed my neotherm somehow got bumped to 82. i moved it back down to 78.

i dont have alkalinity or calcium test kit, but ive been dosing a teaspoon of kalk in a gallon of RO/DI everyday, and a sodium carbonate, sodium bicarbonate mixture every other day. the kalk is not my top off, i use regular RO/Di wtaer for that.

Now for the real problem:

yesterday and today i have come home to an unhappy stylophora and trumpet (see images attached). my margarita snails seem to keep falling and landing on their backs, with all their insides still out, but unmoving. my hermit crabs are responsive to touch, but are on their backs too. my feather duster was 1/2 out of his tube. i turned off the flow and he pulled himself back in. my damsel is still okay, unsurprisingly. idk if i could kill him if i tried.

any help/advice would be greatly appreciated.

also, i am running biocube skimmer, carbon, zeolite, and biomedia in a filter bag. my flow is rated at 132 gph in my 3.7 gallon cube.

you need to get alkalinity and calcium test kits and test. Alkalinity can get used very quickly or sometimes not, every tank is different. alkalinity is the most important test to do. without testing you could be way high or way low. some tanks can get away with weekly water changes to replenish but all tanks with lots of coral will need constant dosing of alkalinity/calcium. The only way to know if you're dosing properly is to test daily until you become accustomed to the demand of your tank.

I would suspect your overdosing a 3.7g biocube. If you can't test for it don't dose it.

and lean your salinity down to 1.025

Is dosing even needed with the amount of coral in his 4 gallon tank ?

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No way to know if dosing is needed without test results.

Yea I wouldn't be dosing anything without being able to test for it. How can you know how much to actually dose?