Grit in humidifier tub No clue as to cause - Mystery solved

[Grandpapa-G]

I have always used only distilled water from the local Walmart in my humidifier reservoir.  My present procedure is to top up the water level daily and completely rinse, fill with fresh distilled water check for signs of contamination every 3 weeks, and carry out a  more thorough cleaning (Dawn dish soap/water, rinse and refill) every 2 months.  I have had no real surprises.  A few times I have seen signs of mold around the corners of the gasket or I think I feel a slight slipperiness at the bottom so I switch out the tub for a spare and do a more rigorous clean and dry thoroughly.  Last night when checking the tub I noticed what felt like grit all over the bottom of tub.  Warm water and dish soap did not remove this layer.  Close inspection revealed the entire bottom an sides up to the usual low water line (morning level) were covered.  I was able to remove most of the grit with persistent gentle scrubbing with a non-metallic scrub pad (used for dishes) but more work still needs to be done on the corners and tight spots. I have no clue what caused this.  It was likely present for at least a week but did not seem to affect the leaks, appeared to be clear, and could not be observed under a 10x loupe that I have used, in the past, to examine crystals down to 20 microns.  Has anyone seen this before or have any idea what it could be?  
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Mystery Solved
Last night I used a spare tub and before posting this thread I check this tub - It too was covered in grit.  I turns out the water bottle I opened recently was spring water.  It was one of three bottles I recently purchased from the distilled water section they all look the same but one was labelled spring water.  I now have two tubs to scrub and am down to using my last tub - the one from my travel machine.  I guess one of the mineral salts has precipitated out - it was an easy way to grow microcrystals.  I doubt any harm was done as the water vapor that passed through the machine should only have a small amount of salt.

[DeepBreathing]

A good soaking in vinegar followed by some vigorous scrubbing should get rid of that mineral scale.

A thin layer of scale won't be deleterious in the short term, but you don't want it to build up. It won't hurt use a scaley tub for a while.

[SleeplessInPHX]

A good soaking in vinegar followed by some vigorous scrubbing should get rid of that mineral scale.

A thin layer of scale won't be deleterious in the short term, but you don't want it to build up. It won't hurt use a scaley tub for a while.

I agree with DeepBreathing. The water here in the Southwest United States is HARD and full of calcium and other minerals. 

I recently purchased a couple lightly used ResMed Airsense 10 humidifier reservoirs. The reservoirs had hard water scale in them. I filled them with standard white vinegar and let them sit overnight. Cleaned them in the morning with my dish sponge and anti-bacterial soap and it wiped right off.

You may find white vinegar in your store's laundry detergent/cleaning products section far cheaper than the food-grade vinegar. 

We have to do this to our coffee pots. Faucets. Tubs. Everything!

I have a reverse-osmosis water purifier system and exclusively fill my CPAP humidifier reservoirs (and coffee maker   ) from that. No scale or calcium buildup whatsoever. I also final rinse with R.O. water when washing my mask and hoses. No water spots!

Good luck!

[Grandpapa-G]

Thanks to DeepBreathing and SleeplessInPHX,
You are correct, Just 1 hr soak in white vinegar and all clear - no scrubbing necessary.  I'll be more careful shopping for distilled water in the future!

[Sleeprider]

The best way to avoid this problem is simply dumping the water in the morning and a fresh fill daily. By reusing water, you greatly increase the risk of a bacterial infection (pink slime) in the tub, and you are unintentionally concentrating the mineral content of any water you use. I have never had problems over the past 12 years using tap water, but dumping the water, and wiping out the container prevents a lot of problems.

[SleeplessInPHX]

The best way to avoid this problem is simply dumping the water in the morning and a fresh fill daily.  By reusing water, you greatly increase the risk of a bacterial infection (pink slime) in the tub, and you are unintentionally concentrating the mineral content of any water you use.  I have never had problems over the past 12 years using tap water, but dumping the water, and wiping out the container prevents a lot of problems.

Good point! 

(SleeplessInPHX goes off to dump and rinse humidifier reservoir...) 

[Big Guy]

What Sleeprider said! 

[Grandpapa-G]

Sleeprider,
I agree that your suggestion clearly lays out the "best practice" for care of the humidifier but it would not have prevented my problem.  In my case, once I noticed the problem I switched out the humidifier tub for my clean spare, filled it with fresh water (what I believed at the time, to be distilled) and the next day it too was coated with grit up to the low water line with precipitate.  It was only then that I discovered that one of the three bottles I purchased was Mineral Water.

[Sleeprider]

Well, yes! Mineral water makes a great drink, but kinda works against you in an evaporative humidifier. The same water with a good whisky or gin on the rocks should be perfect.

[RNeil]

Something is wrong if you get mold in the reservoir. I wipe out the reservoir every morning, then store it upside down so any residual water can drain or evaporate.