I've had a softener for a few years. Does it makes sense that my hot water is testing harder (just a little less soft) than my cold water? Cold is clearly 0 and hot shows maybe 25ppm. I'm using test strips. Water heaters are one year old and I haven't drained them.

Well, I'm going to assume your softener is before the only point of entry for your house water supply. As such, no, I doesn't make sense to me. I think I would start looking for a stoichiometric answer. Your water isn't harder I don't think, but I do know that when I measure specific gravity during wine making there is a temperature variance that you have to account for if the must or wine is hotter than 60C. So, it stands to reason that your test strips may need or require a differential based on temperature.

Here's a question, are you measuring out of the hot tap? What if you let that hot water cool to room temp? Same reading?

In the flip side, it's possible your soft hot water is absorbing the high hard water precipitates if any existed.

It's not a temperature issue. My hot taps don't provide hot water instantly. Test strips provide the same answer with cold water from the hot tap and hot water from the hot tap. I also checked by testing the 170 degree water from my RO system and it was zero just like the cold RO water.

The softener piping connects between the line from the water meter and the entry to the house. The connection is in my front flower bed and I didn't visibly see the work.

I just tested water from the water heater drain and it's the same hardness as the hot tap. I will test the cold inlet of the water heater and see what I get.

Alright, so this has been bothering me.

I had a couple of ideas…

Have you tried with different methods other than strips? Perhaps the strips chemistry is providing a false positive of sorts and measuring something that is leaching out of the wall of your water heater?

That line of reasoning lead me to thinking "what is in a water heater that can leach out and be read by a test strip?" Its pretty much the steel tank and the anode rod is all that's in contact with water ….

You have a sacrificial anode rod in your water heater. So I did some reading and it turns out those are made of aluminum OR MAGNESIUM. Magnesium being the most common kinds dur to its ability to prevent steel from being eaten away because magnesium more freely gives off electrons.

Since magnesium is one off be major components to water hardness other than calcium, my working theory is that your water heater has a magnesium rod and as it's decaying Mg is released into the hot water and that is what your strips are picking up? Also maybe why temperature doesn't matter.

That's the best I got. It's interesting to me, so I'm curious to hear your results.

Confirmed the inlet to water heater is zero. Must be the water heater.