The decrease in pH in the aquarium, why?

The pH in my area is between 7.6 to 7.8. When I was setting up my tanks, only I used the silk plants, and rock cave decorations that were made for aquariums (I have thoroughly rinsed.) I substrate an established aquarium gravel and glass stones (To be inert). However, my pH is reduced to 6.4 in my tanks. I took the decoration of each and individually tested for 24 hours in a container water to see if it would decrease the pH of the water, but each one seems sure. Since I was trying to get the tank to cycle and to treat my water for changes in routine, I use Stress Zyme, Cycle and Stress Coat. Also add 1 / 2 teaspoon salt for each gallon of aquarium water. Do any of these products make that the decrease in pH? Why the drop in pH, anyway? The 5-gallon aquarium is also a strong bacterial bloom, but I do not think it in any place near the bike finish …

man relax and stop releasing chemicals in your tank. How do you know that is a cycle if you keep nosing.

new tetra silk plants installed in aquarium

Vibran-Sea Soft Foxtail Silk-Style Aquarium Plant, Large 13-14 tall, Electric Blue $8.69 BLE PLNT SOFT FOXTAIL BL LG…

Silk Halimeda Copios Lg Aquarium Decor $7.99 The SeaGarden Aquarium Dcor offers a line of realistic-looking ocean plants. The Halimeda Copios are amazingly beautiful plants that you can enjoy in your aquarium. These life-like silk forms sway in the current with a weighted resin-rock base to maintain plant position. To use, rinse the plants with warm water before placing in your aquarium and rinse again when cleaning is needed….