Club soda manufacturing process and problem in quality

How to increase $$\ce{CO2}$$ gas in club soda? I am planning to start a PET bottled club soda industry. My process involves chilling the water up to about $$\pu{4 °C}$$ and filling under pressure up to $$\pu{4.5 bar}$$. Of course, once the bottle is filled, pressure will be released to facilitate capping. That is the standard procedure to fill club soda in PET bottles. With this I am unable to produce a good club soda.

Here the problem as per customers is once the cap is opened and only half of the soda is used, capped again, refrigerated, but there is no $$\ce{CO2}$$ gas found for the second time use. However, in other brand soda, they say, there is still gas in the soda for the second, third time use......

If I increase the pressure to $$\pu{5/ 5.5 bar}$$, the PET bottles exploded....

How to overcome the difficulty? How to ensure my club soda will have gas in it for the second, third time use...

What minerals can be added to water for good flavor and taste of club soda with dosage?

• Perhaps trivial question, but do you allow enough time to establish gas dissolution equilibrium at the high pressure ? – Poutnik Jul 6 '19 at 6:06
• I'd recommend you buy yourself a regular club soda machine and see how it works. Although why you'd want to reinvent a product that is already on the market in millions by several producers, I cannot imagine. – Karl Jul 6 '19 at 7:48
• @Poutnik I was going to ask something similar. Simply applying pressure doesn't guarantee dissolution. Effective mixing also helps by increasing surface area – Beerhunter Jul 6 '19 at 20:35

Most generally used two-liter PET bottles for soda bottling begin to fail at pressures around $$\pu{10.34 bars}$$ (1034 kilopascals), or $$\pu{150 psi}$$ (pounds per square inch). This pressure, at which the bottle will burst, is more than it would normally encounter during packaging or normal use.
This pressure is also much higher than you needed to have in order to make a good soda (~$$\pu{6 bars}$$). So, find the provider who can make the bottle with the thickness of usual 2-L plastic bottles.