Red Cherries - months later, still dying

So I'm at a -total- freakin loss here. I keep my tank super clean. I don't overfeed, I don't underfeed.. I usually give about half a sinking wafer every other day, sometimes every 2 days. I have a 10G with 14 or so RCS, a decently large mystery snail, 6 dario dario, maybe 10 or so scuds that no matter how many times I suck them out with a turkey baster they keep reappearing, a couple small ramshorns and a few pond snails. Sounds crowded but its a pretty densely planted tank with two pieces of driftwood and a lava rock so lots of places to hide and there is never any ammonia. Nitrates/ites are always like non-existant. I have one of those in tank monitors + I test every couple days too.

Gravel is eco-complete..

Stuff I put into it:
Once a week-ish I dose 1 cap of flourish
Once a month-ish I do a small dose of tetra florapride
I want to say a few months ago I put in a couple sea chem root tabs
Every couple days I do one drop of kent iodide & 1 drop of kent calcium
I use tetra aquasafe for dechlorinator
Sometimes I use ph down during water changes - I put the drops into 1 gallon plastic water jugs with the tap water and I let it sit for a few hrs before I put it in..

The ph here is unusually high, it's about the only thing I can think of that's causing them to die, it's like 8.4 here.

So I went for like 3 weeks with no shrimp deaths and suddenly tonight I look in the tank and since earlier this afternoon when there were 0 dead shrimp, there was now 2 dead shrimp, an adult and 1 young adult/juvie. Neither looked like they were overly damaged but they were somewhat nearby each other..

I am so at a loss. I thought I had it under control. Now everytime I walk by the tank I will be paranoid and check the tank for dead shrimp 20 times a day again. Argh.

So I have read like all the labels and there is no copper .. is it the ph? They've been in the same water now for a few months.. why die all of a sudden?

no no haha i change it quite often. 1-2 times a week, 2-4 gallons each time. i meant like.. same ph/perameters etc. i am freakin diligent about watching my perams, and i have one of those battery gravel washers too, so my tank is really clean.. i dont get it

Hmm I had considered the peat pellets but I didn't get them *yet* because of the water color change you get with them. The GH is usually around 75ppm and the KH is always like 300ppm. The PH is 8.4 right out of the tap. They have not reproduced at all due to the water, and I'm alright with that because I have given up on the idea of breeding them anytime soon. But I would at least like them to stay alive

All of my snails are doing just fine, thriving even, they breed like bunnies and grow insanely fast. My mystery snail went from the size of a penny to like 2 inches across or something, within 3 months. My dario dario's which like lower ph, are healthy, active, no signs of stress, happily chasing down any live food they find in the tank or standing guard over the brine auto feeder waiting on the brine babies to pop out. Both of my bettas in another tank are happy and healthy. It's only the shrimp having problems.