Kh fell through the bottom Help

If you are not keeping any "exotic" shrimp but only RCS...then it's likely a mix between your messing/w the water, excess ferts like wicca suggested, and perhaps too high or too long on the lights.
Keep in mind that most chain store pet shops, though luck perhaps grants them A person who is somewhat knowledgeable, usually lacks people who are more than
curious about what they sell.
Point being they seldom have anything but the same tap water you have in those tanks. So those shrimp ae used to that. Things could be different as you may have
gone long and far to get the shrimp for example.
But changing to distilled water didn't just lower the PH it took out a lot of what shrimp need such as TDS which theoretically you put back.
I would suggest you test the tap water for PH and if it's not like 8..consider putting
it back as your water. But if so make the change by small(20-25%)water changes weekly. But till then I would start by doing a 50% WC now and not putting back any ferts till you read up on them as you don't have all needed ferts and missing components stop plant growth. BGA is next possibly. Learning how to use a fert calculator(first thread in the fert section) and using what ferts as are listed as "EI Low light/Weekly" would be my suggestion for that amount of plants/size tank.
You will find that title under "and I am dosing for" in that calculator.
I believe that full EI would be way excessive for your tank.
All plants take ferts from the water. Java fern should not have it's Rizome planted but
only the roots which hang down from it.
What light is on there and for how long ?

The shrimp are from the Shrimp Farm. I'm assuming he probably has perfect water params. My tap water was ph 7.8 to 8.0 with 465 TDS and I was losing a lot of shrimp in my main tank. I'm cutting that water with distilled now and things are much better. Yes all of my ferns are tied to rocks or the mopani wood. My light is a fluval LED plant and it maybe on too long at 10 or so hrs. I'm dosing with api root tabs, 3 in an 8g tank which is a little under what they suggest. I use 6 or 7 in my 13g with no co2 and huge growth. I'm not too worried about the plants as I have 2 other tanks full of plants to replace any I may lose in the shrimp tank. I am using just distilled and adding saltyshrimp gh/kh and seachem neutral in the shrimp tank. Ph in that tank seems to be in the 7.4 or 7.5 range now with the neutral. Only the last few days have I added flourish potassium in an effort to raise the kh. It doesn't seem to affect kh at all though. I mix the water up in a 5 gallon bucket before water change and check it with tetra test strips. I ordered a ph meter and it should be in next week. My TDS measured 288 this morning. I'm doing w/c about 25% once a week. It is a new tank, instant cycled with bio-max from the other tanks and I was told that maybe why I'm having to add neutral regulator as ph is higher in the tank than when I mix it. My concern is the kh. I'm assuming it maybe the plants taking up too much potassium as I noticed some yellowing on the new hygro growth. It measures in the moderate range, 80ppm, a little darker in the make up water than in the tank so it's definitely losing potassium in the tank. It's not in the danger zone but I'm used to it being much higher in the main tank. I'm afraid of ph swings mainly at night. The shrimp hide in the moss most of the morning and only come out in the afternoons. They look fine then. I haven't seen any little floating bodies but I never see all 16 out at one time either. Really I hate messing with water chemistry at all and this is the 1st time I've ever had to use distilled as my old house had perfect well water. I REALLY don't want to add baking soda to the water as is suggested in a few articles. It raises ph and I'm perfectly comfortable with 7.4 or so as it is now. I'm just hoping someone in the forums may have a suggestion or seen this in one of their tanks.