One of the first things I bought were x2 Marimo, when they arrived not having any Marine salt I put them in a jar of still spring water, under a 6500k light, almost instantly they started to form small bubbles and a few hours later they started to float, turned the lights off and next morning they'd sunk but started to form small bubbles as soon as I turned the lights back on, and were floating again, after a few hours. When I set the tank up I made the water in their jar SG 1.005 as a start to acclimatize them to the tank at SG 1.012. They instantly sank and for the last couple of weeks they've stayed on the bottom and not formed any bubbles, though they've stayed green. Today I took one out of the SG 1.005 water and put it in a jar of still spring water, instantly it started to make small bubbles. I don't think they like salt ? and just shut down to wait for a change of water ? Plan 'B' is to set up a small fresh water tank with x3 White Cloud Mountain Minnows and the Marimo next to the Shrimp tank.
SG 1.005 1/2 hour back in spring water
SG 1.005 1/2 hour back in spring water