Been working for a while on an idea to incorporate a kind sump to add water volume, and perhaps a little nutrient absorption, to my all in one Red Sea tank. The idea of a ball of Chaeto floating in it would be interesting. But, if it sinks, not so much...
The thicker it gets the heavier and then it sinks. Make sure you tumble it often. You will also have to harvest it as it grows quickly under proper conditions. I harvest about 1lb every 2-3 months.
My Cheato just chills. I think if it is going its job by sucking up bad and putting out oxygen then shouldn't it float? Be forewarned however that cheato rarely forms a perfect ball, and it will eventually fill the tank it is in and be touching the sides and bottom, then if it was floating you will never know
Move it around-tumble it around. I stretch mine out so it's not such a tight ball-helps it grow and distributes the light evenly. I'm a plant person but it should at least be tumbled.
Cheato needs a lot of light. I have a 3G fuge with a 24w cf sitting right on top of it. I run the light opposite my DT lights (at night) for 8hrs.
Cheato like any other plant needs care in order for it to do what we want it to. Good lighting, good low flow and some TLC.
I use a cheap DIY home depot 6500k. It works better then my my old compact fluorescent fixture. I just rip some off and feed it to my tangs so it dosn't over grow.