Hydrofill Question

Yes any purified water RO, distilled, DI will be hungry, low ph, maybe in the 6's.

In a heating system that low ph water will grab some of metals in the system and balance back to a neutral, non aggressive ph. This happens within a few days, it does not attack the metals to the point of causing harm. Also exposure to air will change the makeup of pure water. You just need to move that ph into the 7's to be neutral.

A few other options, add a hydronic conditioner to the filtered water. A 12 oz spray can will do about 35 gallons of fill water. Fernox, Rhomar and others have cleaner and treatment, two can kits. The hydronic conditioners will immediately buffer that ph, take it a bit to the alkaline side, scavenge any O2, add a micron thin film on the new components to protect them.

Modern hydronics may have copper, various brass alloys, steel, cast iron, various stainless and possibly aluminum alloys, you need to protect all those with a multi metal conditioner to protect the investment and maintain warranty coverage. Conditioners, properly used are extremely cheap system insurance.

When you buy quality brand glycol, all those ingredients are blended in.

Use a cleaner first on any new or rebuilt system, need to get oils, dirt, flux, etc flushed out, many flux continue chlorides, not good.

Blend the water when you put it in, no need to put 100% pure DI water into the system. All the boiler manufacturers have water spec, stay within their hardness, ph, conductivity, TDS recommendations.

The hydrofill can take it down to near 0 TDS, as indicated on the meter on top. I say stay under 100, some say under 30 TDS, see what your brand recommends for acceptable TDS.

Window washers use DI so they get spot free windows without needing to dry or squeegeeing them after washing. DI water works great for rinsing you vehicles after washing, a spot free result.

Here is Rhomar recently updated manual for water treatment, hydronic and steam.

My test kit is a simple softness tester, the test tube type with the 3 reagents, just count the drops
A stick type, digital ph meter, good for water and glycol
A electronic TDS tester
A refractometer for glycol.
A few hundred bucks worth of testers will get you the most important numbers to watch.

Meters do need to be calibrated yearly or so depending on how much you use them. Usually sample packets of test fluid is included in the kits.

If a problematic system needs more comprehensive testing I send it to Rhomar or other pros for analysis and recommendation. If you need to know exactly what is in the water for a warranty claim, or liability issue, for example.

We did a few videos and Coffee with Caleffi webinars on filling and purging in general and a few on the HydroFill, should be posted on the Caleffi You Tube channel.