New to this world

[Ktruong]

Hi All
New and excited to learn this hobby
I ve just purchased a second nano one marine 36 badly kept. I believe there were every kind of algae species more bad than good in this tank. There were black,red,and green. Living among them were a few snails,a Cowrie snail, one poor Yellow damsel and one sea cucumber.
I was very frustrated and so transferred all the old water to a bucket and move all the fish across., spent 4 hours cleaning everything including the sand. Until it was almost perfect then transfer everything back with 20% top up of saltwater. Ok water look great fish seem happier. I m feeling abit better. But when i spoke to my cousin (many years running a 400 l marine tank)he advise me differently. Anyway my concern is that since i put in the sea cucumber back in it seem to be unhappy and climbed up to the water surface and now blowing bubbles. Can someone please tell me what wrong with it and is it dying? Currently it is on the glass and head semi above water.

[SantaMonica]

Very late welcome. Do you still need this help?