Water Chemistry in a Closed Loop

It can't be done by dosing at those sorts of conductivities. At low conductivities, there is very little in the way of ionic species in the water to give anything other than a neutral pH. Anything that is added will raise the conductivity. So, dosing is a non-starter.

Why is pH correction of any value here?

As you need a very good ion exchanger to reach down to this low conductivity, nearly all ions will be gone.

So what may bring your pH outside the desired range?

Ask the experts at Prominent, Heidelberg (and send them my greetings).

RHABE

It is impossible to give you any advice without knowing what your application is and what your key control parameters are.

As an example, for generator stator coolant systems you can generate sufficient sodium ions to control your pH by adding a sodium form mixed bed.

For a other applications a solid alkali such as sodium hydroxide or a volatile alkali such as ammoniaor morpholine can be used.

For single and two phase systems a polyamine blend of neutralising and filming amines can be used.

That said, none of these can be implemented without increasing the specific conductivity of the solution, although it can be done without increasing cation conductivity.

One other thing, dissolved oxygen saturation point is ca. 7 - 8 ppm. How are you achieving 100 ppm?