The Marimos are recovering from their unpleasant bout with slime. They came with an attractive white sand-like substrate. Unfortunately, the substrate stuck to the sides of the Mos. (You can still see some of it clinging to them)
When I gave them their summer clean-out, I decided to put pebbles in the bottom. Pebbles that I had previously used in the bottom of a planter for extra humidity and which had been outside for a year and were a little green. I washed them off, layered them in the glass and put the Mos back. Over the course of the fall the water gained a slime covering which drifted down into the Mos' space.
I woke in the middle of the night with horror (not an uncommon occurrence). Slime was growing in my office and choking my Marimos.
I lay awake formulating a plan of attack. Could the slime be blue-green algae, toxic to those who might drink it? I resolved to bury the slimy water in a hole, rinse the Mos before restoring them to a pristine bowl.
The next day I prepared for the attack. I went to the dollar store to get a strainer, slotted spoon and bucket. I went to Goodwill to get a new, bigger container.
I dug a hole, put a hanger around the strainer and balanced it over the hole. I drained the mucky water off and rinsed the Mos with water from the bucket. I couldn't use the hose because we were having an unusual bout of freezing weather and the hoses were stiff with ice. The Mos were put into their new larger container with nothing on the bottom in case the slime came back.
It's been a month and all seems to be well. No slime. So far.