As per P. 48-49 of the Diesel Supplement:

Coolant additives
At specific mileage intervals of 15,000 miles (24,000 km), as listed in the
scheduled maintenance information chapter, the coolant additive
should be checked. The optional message center, if equipped, will also
display the message CHECK COOLANT ADDITIVE at this time. The
purpose of checking is to verify the correct concentration (freeze point
protection) and additive strength (corrosion inhibitor) levels of the
coolant for maximum engine performance and protection. Three
products are available for ensuring the life and health of the coolant: two
test kits and a coolant inhibitor additive:
• Rotunda 328-00007 (Matthew’s Water CoolCheck) – Evaluates water
quality (hardness, chloride, and pH) for 50/50 mixture of coolant and
distilled water. Use distilled water. If distilled water is unavailable,
water meeting the requirements of Rotunda 328-00007, is sufficient
for vehicle use. Using water that fails to meet the requirements can
lead to coolant passage scaling and degrade the engine’s durability and
performance.
Rotunda 328-00008 (Antifreeze Coolant ELC Contamination Kit) –
Evaluates the coolant concentration (freeze point protection) and
additive strength (corrosion inhibitor) for overall coolant health. Note
that the first step is to verify that the vehicle’s coolant concentration
is in the window of 40 – 60%. If the concentration falls outside of that
window, the evaluation of the corrosion inhibitor strength will not be
valid. If the report results in a pass the cooling system does not show
excessive contamination. No action is required. If the report results as
insufficient, the corrosion inhibitor (additive) strength of the coolant
is too low. Add entire contents of one bottle of Motorcraft Specialty
Orange Engine Coolant Revitalizer to the coolant reservoir. The
coolant can be recharged with this additive up to two times before the
coolant must be changed-out. When exchanging the full coolant
volume, the system must be flushed and refilled with distilled water
and coolant concentrate (Motorcraft Specialty Orange Engine
Coolant).
• Motorcraft Specialty Orange Engine Coolant Revitalizer(VC-12)– Additive to
boost the corrosion inhibitor level based upon the test results of the
Antifreeze Coolant ELC Contamination Kit. The revitalizer may be
added two times over the life of the coolant. If additional dosages are
required, the cooling system must be flushed and refilled with distilled
water and coolant concentrate (Motorcraft Specialty Orange
Coolant).

I recieved confirmation that Acustrip is the OEM for the test strips, and they can be found here. They are listed under "Contamination, Red Extended Life Coolant"

Acustrip Antifreeze Coolant Test Products