Bubbles, Always On? Or Off At Night?

Yup I did. That bubble wand would cover most of the back of my 200l, does it need weighing down?

It keeps it's own weight down once submerged and empty of air, but it is more buoyant than an airstone so as I said it is a tricky thing to get buried in substrate. The flexibility of it means you push one end down and inadvertently bend it, so when you move along and push the next bit down, the far end pops back up again!

Once it is under there (I had to use my lump of bogwood to hold one end down while I buried the rest) it stays down and does not lift when the air is introduced. The bubbles it produces do vary slightly but there are no large ones that give off louder popping noises, it actually creates a bit of a "fizz" at the surface... Great product...

Littlefish/Fiona: if you want to take your dwarf puffers' entertainment to the next level, you might want to consider this the R2 Fish School Kit (available via Amazon). 

It might make it easier to clean, so I'd be very interested to know how you get on. I do have a soil substrate topped with sand in that tank though.