Increased pH of permeate water in Reverse Osmosis plant with 25 m3/d capacity.

Hello All

The pH input to the reverse osmosis system is7.5
While the pH of the output water (permeate) reaches 8.9.

Note:
1- Only acidic antiscalants are injected.
2-This RO system designed in a room that its has a high temperature approximately in the range of 33-38 ° C.

Questions:
What is the cause of the pH increase?
A- Temperature has increased the pH?
B- Does microbial contamination can increase pH?(Chlorine injections have not been applied, which makes the water bad smell. membranes has also been infected with microbial contamination.)