These little fish contain small quantities of silver (as noted right on the package) as an anti-bacterial compound to slowly dissolve into your humidifier's water. It works well for slowing the growth of biofilms in your tank and filter. However, as some other reviews here noted the silver will stain the water's path toward the filter and the filter itself a grey-ish color. It shows particularly much on the white plastic of the tank cap, filter housing, etc. I don't mind, as some silver-salt stains are much preferable to slimy biofilm, both for the quality of my indoor air and the humidifier's function and longevity.

My daughter thinks that a fish in her humidifier's tank is cute. I've put this item on subscription for the winter months.

I have been using evaporative humidifiers for years and these really do help to keep your filters from growing mold or other gross stuff. I think they work sort of the way that charcoal works to keep water in a fish tank clean.

First off I have seen people complaining because they can not get these in the tank of their steam/warm mist humidifiers.... You do not need to use this in any humidifier that works by heating water up to the point of steam because trust me. Boiling water does more to kill mold and bacteria, so save your money.

I guess that you could use them in ultrasonic humidifiers but mostly these are good for using in with filters that utilize a wicking filter. These paper filters are notorious for collecting mold, so this is a great item for keeping these type of humidifiers clean.

They are super easy to use and I find that they work for at least one season if not longer. So even though they can be a little pricey they do last way longer than your filters will.

The little fish is super cute in my humidifier. It's designed to stay upright and the top portion floats while the bottom part stays in the water.

All you have to do is put it in the water and it should keep working for quite some time. If your filters start getting dark or red stuff on it then it's time to change to a new one.

Thanks for reading my review.

Becky Brooks

I have a 2.8 L humidifier that I was having to clean every day because of pink mold. I was hesitant to buy these fish due to mixed reviews. Granted it's only been 1 day since I put it in the tank, but it's the first day there's no pink residue. I cleaned the humidifier with peroxide & also put a cap full of it in with the water for the first use along with the fish. Mixed reviews may be based on the type of mold/fungus you have.

My humidifier requires frequent cleaning because it is filter-less. Every week or 2 you are supposed to clean it with vinegar and/or disinfect it with bleach.

If I let it go 2 or more weeks without cleaning, it seemed to accumulate orange gunk. I decided to add the fish because of this. Recently it has gotten warmer out and I no longer needed to use the humidifier. Admittedly, I left it with water in it for probably 2 months because I didn't feel like cleaning it. I just opened it up to clean it for the summer and to my surprise, NO GUNK AT ALL. Before the fish it would have orange build up after just 2 weeks and now it went months with the fish in it and didn't build up orange gunk.

Next winter I will definitely be stocking up on these to use throughout the season.

This is really cute. But you do need a humidifier with a wide opening. I wish it bobbed around more but it doesn't. Still much cuter than the capsule shaped ones that I usually use. I'll probably go back to the capsule type because they cost less but this was fun to have for a while.