How did you lower you pH?? How are you bringing your pH up?? What substrate do you use with your TB’s??
I don’t think one has anything to do with the other. Low TDS means your water is clean and has little dissolved solids low pH is acidic water. My CRS SSS bread like rabbits in low pH 5.6-5.8 at one time I had 16 females berried. I had dieing adults but ton of babies that I did not see, I found 6 panda/ BKK While breaking down my tank it took me 6hr to fish all the babies from the moss.
“Now ADA is like stiff mud at the bottom and 50-60% whole grain in 1cm at the top.
I'll stop UGF tomorrow and will add prefilter sponge to the outtake. Hopefully bacteria die-off won’t kill tigers.” Your filter will have bacteria you should be ok and the stuff in the substrate won’t die that quick. That is why I only did like 30% UGF in the tank.