chemical burn from tap water. Switch to bottled water or rain water.

Also flush the soil to rid it of excess salts.

I agree that it looks like burn, but these plants are rooting in straight well water, and I don't believe the leaves have ever been wet. It's a good guess, but I don't think that's it. If the water were an issue, other plants in soil would be affected, but only these are.

The problem in the picture isn't bug or disease-related. It's due to a problem that originates in the roots. If you never allow the plant the plant to wilt from under-watering, you can eliminate that possibility. That leaves over-watering and/or an excessive level of dissolved solids (salts) in the soil as almost certainly the cause.

If you aren't using a soil you can water to beyond the saturation point, so you're flushing the soil when you water, without having to worry about the soil remaining soggy so long it affects the root's ability to function normally or the saturated conditions causing root rot, you'll be in a constant battle with your soil for control of the plants state of health. A healthy plant is not possible unless you can keep the root system happy. You can put two-bit plants in a ten-dollar soil (a structurally stable, well aerated soil) and have a beautiful planting; but, if you put a ten-dollar plant in a two-bit soil the outcome highly favors disappointment.

If you want some soil guidance that will make healthy plants something you can count on, rather than relying on the odd serendipitous outcome, let me know and I'll provide some links.

Al

Al, these aren't in soil. They are cuttings in water. The only root is a tiny nub just beginning. No other plants are affected. They didn't have the brown spots when still on the plant. They've been cut about 3 weeks. I noticed the spots today.

Is there something about rooting pothos in water (specifically THIS water, since I've rooted pothos in water many times before elsewhere) that's causing it? If so, what free (or very nearly free) pet-safe options do I have for rooting cuttings?

Thanks

BTW, I'm making a batch of your gritty mix. I just don't have the money for the final ingredient yet.