The first time I used RezBlock, I did so in my hydratube.
I left it in there (I thought it looked pretty sitting "at ready")
I never used the Cloud much.
After a week of sitting unused, a "colony" formed as Caligula described.
It was inside the Hydratube however, and was in the form of a rubber band.
At the time I even called t-dub in for advice on how to remove the colony... as it wound itself in the holes of the hydratube.
Iso made it into a white rubber band that I could not shake loose.
After a few days of shaking and trying, I made a fish hook out of a few pipe cleaners.
I finally caught and extracted the "rubber band looking" gooey string.
I never left the stuff in there again except when I was about to use it.
I do not like water filtration at all... so it is not an issue.
When a visitor is here and wants water, I mix the extract on the spot, and empty and clean the water piece the second the session is done.