Mass Shrimp death all dying 24-48 hours after molting

I've officially lost all my shrimp after 4 months and I am feeling incredibly sad and lost on what to do.

I have a small planted 6gal that is shared with by 6 strawberry raspboras. I had a huge algea problem I was trying to fight off in mid December. I had berried shrimp and didn't want to do a water change to stress the shrimp or newly hatched babies.. later on I foolishly did a larger water change with distilled water without drip acclimating it because I wasn't thinking and was panicking over my plants all dying and thought after the babies got a wee bigger they'd be ok for a water change finally because the black outs and manually removing the algae wasn't enough anymore. My biggest mistake was probably using the Algaefix(maybe 2mg?like 1/3 of a cap) not realizing it wasn't safe for shrimp..Ive used it before without issue so I didn't even realize.

Immediately the babies started dropping like flies and probably all died off within three days of the water change. I didn't have a gh/kh kit at the time but API testing was all still normal range and it's around 74ish degrees.(We did lose heat for about 48 hours so the water was around mid 60s but I didn't see any new deaths those specific days) Every few days I'd find a molt and a dead shrimp nearby.I only have about 3-4 shrimp left and I finally bought a kh/GH kit and did initial testing of everything.

Distilled: GH-8 KH-6 PH-6.4 Tap: GH-10 KH-7 PH-7.1 The tank: GH-19 KH-13 PH-7.4

I SLOOOOOOOW dripped acclimated this time probably over 12+ hours in hopes to save the remaining shrimp because the GH/kh were so freaking high New results I got it down to: GH-12 KH-6 PH-7.1 And then over the past few days I've been drip acclimating a small masons jar full of distilled over several hours.(Gh-9ish,KH-7)

So after 3 weeks of this, all my shrimp are dead now. I thought I'd have at least one survivor, lasted two days after molting, acted normal, was grazing and hanging out. Found him dead this morning. And after FOUR days somehow my GH went back up to 18,KH-8 and PH-7.4. The only thing I can think of is that I have a few rocks that are literally glued together as part of the terrain/environment that I originally got from the beach like a summer ago and I've had these rocks in the tank since September. I also use aqua soil and sand. And I can't imagine the initial algae drops are still responsible?

For any drops of anything else, over these few weeks I've done potassium drops for plants trying to get them to recover, the shrimp minerals for the new water and the water conditioner when I mixed tap and distilled.

The tank itself is looking much healthier and the fish are still the same and are acting normal. I've somehow got a ramshorn problem now, and I think there must've been some eggs on my heater from another tank(I put it in the shrimp tank at one point and took it out after a week because I wasn't sure if it was contributing to shrimp deaths) again, the shrimp have all primarily died about a day or so after successfully molting.

I'm incredibly discouraged after making careless mistakes after mistake. I really enjoy the shrimp. I want to make the tank habitable again for them but I am at a loss and it makes me feel like I'm not cut out for this hobby. Does anyone have any insight?