Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Is the hydro cell just supposed to sit at the top of the water? In the tank?
Document: I've had 2 of these units for less than 2 weeks when mold began to appear on the inside of the tube where the vapor exits. There are also two plastic pieces in the tube which guides the vapor. The problem is these 'guides' make it impossible to clean the inside of the tube and the underside of the plastic piece on the top of the tube. I rinsed the tank and the clean the base as recommended. However.
This is a very quiet humidifier. I have not purchased others however, I am very pleased with it's performance so far. The water tank is easy to change and does not leak. For smaller rooms one may want to keep the door open as it does produce a good amount of vapor? Overall I am satisfied and happy I chose this item.
I use filtered water, so I have more room in the tank.It also comes with a sample of their descaler, which is the only item they recommend for that purpose.I wonder if you can't just use vinegar + water to clean it, but I'll do more homework before I try that.I'll update my review after using it for a couple days; but after our very poor experience with the Drop Shape, the U200 is already impressing me.
It does its job, no complaints. There's a light inside that turns red when the water runs out. I fill it once a day when I'm running at about 50%.One other thing I would recommend is to use water filtered through a Brita. No need for boiling. I pre-fill an empty gallon milk jug that I keep in the fridge, and rinse out the tank and wash the base at each filling.
I am so far satisfied with the humidifier. It works very well. I normally keep it on medium setting, and the water lasts for almost 24hrs. It is very easy to fill up the tank( it has a retractable handle to hold the tank while pouring water)  and post it on the base. Very easy to clean,too. I really like the design of the humidifier. The steam opening can be rotated 360 degrees, depending on where you would like the steam to come out.
I even felt like I was breathing and tasting something funny. When I started reading up on how to eliminate the &#34;white mist&#34;, that is when I realized the only way to go was use distilled water. Once I did that, no more white stuff.I like the compact size/footprint. Is very stable on a flat surface, even when my kitten jumped on top of it! It is very easy to refill.
Takes about 90 seconds.Small footprint on my dresser top and for a humidifier, rather classy looking : )
Some of the special features, such as the night light, automatic shutoff, and the fragrance pad take it over the top. Next purchase, we will look into buying one of their larger units.
I hesitated buying this because it is pricey. I'm not at all disappointed! It is quiet enough to sleep with, the blue light is nice and it has a clean look. The small footprint fits on a dresser top or nightstand.
Not heavy or bulky. I love the fact that I can't even hear it. I've purchased many cool mist humidifiers in my lifetime-- this ranks in the top 3.Would definitely recommend.
Answer: no, it usually floats to the bottom of the tank.