Ignoring GH/KH to fix extremely low pH in caridina tank

TLDR; my pH is 4.5 and its neutralizing my bacteria, causing ammonia spikes, just ammonia because the bacteria is not active enough to produce nitrite/nitrates. My plan is to add in tap water rather than remineralized RODI water, just until I get the ammonia and pH under control.

Background:
I recently made another post here
I've been struggling with shrimp deaths and only a few hearty strains remain, blue bolts and black crystal. I have no idea what the cause could be for the pH to drop. Maybe soil, maybe a potted plant that has been leaching fertilizer/ammonia from the rock wool. Nothing changed from when I had guppies in the tank for months. So I am positive that I had a cycled tank. I converted it to a caridina tank without disturbing anything except a water change and a filter swap, but I squeezed out the old sponge on to the new one, and I kept the original filter in with the new one. Yeah I probably reset the cycle by swapping filters, but surely the bacteria were functioning with the water parameters. Now the pH is 4.7 and the problem is the new bacteria are not establishing because (fun fact) nitrifying bacteria are inactive and do not grow at a pH of <5.5. So you can add all the bottled bacteria you want, they aren't going to do anything at that pH. Pure RODI water does not have a buffering capacity (KH =0), so I'm going to use the KH that is in my tap water to add some buffering capacity in my tank and get the pH back to 6. The plan after that is to get the bacteria back up and active so that the ammonia can be treated. Then, when ammonia/nitrite are reading 0's, work on GH and KH adjustments back to the ideal caridina parameters. I feel like the pH, dead cycle, and ammonia are way bigger of a threat than elevated GH/KH.

Current tank parameters:
pH 4.7
TDS 115
GH 3
KH <1

Tap water parameters
pH 7.7
TDS 240
GH 10
KH 4

I'm going to slowly add treated tap water to maintain a pH of 6 and see how things rebound. Has anyone dealt with a pH of <5 before?