Everything is dying

[opalust]

So I had a rocky start to my freshwater shrimp tank, but after a while I got the hang of it. Now, seemingly out of the blue, EVERYTHING is dying.

I started out (once I smoothed out my issues) with 2 Ghost Shrimp, 2 Amano's, 2 Red Cherries, and 2 Orange Bs. I also have two Cory Cats in the tank, which is a planted ten gallon with filter and heater.
First, one of the Ghost Shrimp died in the molting process, so I started adding Iodide to the tank, three times a day (because I have a carbon filter). Everything is good, we even had little Amano babies running around, so I put a sponge over my filter so there were no more losses in the baby department.
SO about a week ago, the remaining Ghost shrimp disappeared, and since the tank is WELL planted, I had a hard time finding its body. Then, BOTH of my Orange Bs.... mysteriously vanished. Then one of my Red Cherry Shrimp (which may still be in the tank, but I have no real way of knowing right now).
Yesterday I took out every plant and though I found the dead Ghost Shrimp, there is no evidence that I even HAD Orange Bs in the tank. No bodies, no shells, nothing. Just gone.
I did a HUGE water change (about 60%), added Prime, tested the water, and all my levels were good. PH was slightly low, but it's always been that way without any problems.
This morning I wake up to a dead Amano, which have been my most durable shrimp yet. All the babies are dead and gone. All I have now is one Amano, and one Red Cherry Shrimp (to my knowledge). Tested the water this morning and the parameters were still the exact same as yesterday. Nitrite and Nitrates are zero, I put in a tab to raise the PH .5, so......
THE ONLY change that I have made since this tragedy has begun is lower the heater temp to about 72-75. I had it set before at 80 degrees, although the water was always about room temp. Could that really be killing my shrimp off like that? I don't have any clue what's going on..

EDIT: Not only this, but the shrimp have been.... not moving. Not interested in food, just kind of sitting there. This is also after I lowered the temperature, and before everything started dying and disappearing. They are still doing this.

** I apologize if this is in the wrong location, I'm just panicking right now. I do not want to lose any more of my shrimp.

[Varanus]

I'm not really qualified to answer, but since nobody else has so far I'll try. It seems to me that if the problems started after you lowered the temperature you should at least try raising it back up to what it was before and see if anything changes, if the shrimp get more active again, etc.

[jonesinfershrimp]

have you checked the ammonia/nitrite levels?

[KenCotigirl]

Why dont you start from the beginning:

How long was the tank in operation before you added fish and shrimp?
What are your water parameters?
What is setup? Sustrate, plants and decor. Lighting.
Temp change should not matter unless it happened rapidly.

[mighty mite]

It's very unlikely a standard ghost shrimp would kill a full grown guppy.

You might have a stowaway. Sometimes you can get a longer clawed ghost shrimp that is a different species. It can easily kill all your shrimp and any small fish you have.

[Mustafa]

Everything is good, we even had little Amano babies running around, so I put a sponge over my filter so there were no more losses in the baby department.

Sounds like you don't really have Amano shrimp. They don't produce babies that run around. They produce floating larvae which die in freshwater (need saltwater to survive and grow).