[BHAVESH]

Hi Everyone,
As it is known fact that when concentration of mineral increases in RO Reject water, pH increases - How we can calculate this?
Secondly, in reject; some bicarbonate gets converted to carbonate, how to calculate this?

[Borek]

As it is known fact that when concentration of mineral increases in RO Reject water, pH increases

Nope. It depends on what is being dissolved. Some things will increase the pH, some will lower it.

[BHAVESH]

Ok, Borek.
In other way, is there any formula to calculate pH based on ionic strength of water?

Secondly, how to calculate conversion carbonate from bicarbonate???

[Borek]

In other way, is there any formula to calculate pH based on ionic strength of water?

Same way you would do with any activity calculations, see for example http://www.chembuddy.com/?left=pH-calculation&right=ionic-strength-activity-coefficients

Secondly, how to calculate conversion carbonate from bicarbonate???

It doesn't convert on its own, I have no idea what you are asking.